title: Android Studio and protobuf Error:(7, 0) Plugin with id 'com.google.protobuf' not found
body: <p>I want to use grpc in Android Studio, but failed in gradle setting.</p>
  
  <p>my gradle plugin version is 2.1.2. I have installed gradle 2.14.</p>
  
  <p>In my app\build.gradle file:</p>
  
  <pre><code>    apply plugin: 'com.android.application'
  
  android {
      compileSdkVersion 23
      buildToolsVersion "23.0.3"
  
      apply plugin: "com.google.protobuf"
  
      defaultConfig {
          applicationId "com.example.test.test_20"
          minSdkVersion 15
          targetSdkVersion 23
          versionCode 1
          versionName "1.0"
  
      }
  
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
          debug {
              debuggable true
              jniDebuggable true
          }
      }
  
      buildscript {
          repositories {
              maven {
                  mavenCentral()
              }
          }
          dependencies {
              classpath "com.google.protobuf:protobuf-gradle-plugin:0.8.0"
          }
      }
  
  
      protobuf {
          protoc {
              // The version of protoc must match protobuf-java. If you don't depend on
              // protobuf-java directly, you will be transitively depending on the
              // protobuf-java version that grpc depends on.
              artifact = "com.google.protobuf:protoc:3.0.0"
          }
          plugins {
              grpc {
                  artifact = 'io.grpc:protoc-gen-grpc-java:1.0.0'
              }
          }
          generateProtoTasks {
              all()*.plugins {
                  grpc {}
              }
          }
      }
  }
  
  dependencies {
      compile fileTree(dir: 'libs', include: ['*.jar'])
      compile 'com.android.support:appcompat-v7:23.1.1'
      compile 'com.android.support:design:23.1.1'
      compile 'io.grpc:grpc-okhttp:1.0.0'
      compile 'io.grpc:grpc-protobuf-lite:1.0.0'
      compile 'io.grpc:grpc-stub:1.0.0'
  }
  </code></pre>
  
  <p>Gradle sync message output is 
  Error:(7, 0) Plugin with id 'com.google.protobuf' not found.</p>
  
  <p>What is wrong in my setting? </p>
  
  <p>I create a new empty project, and app/build.gradle file:</p>
  
  <pre><code>apply plugin: 'com.android.application'
  apply plugin: "com.google.protobuf"
  
  buildscript {
      repositories {
          maven {
              //mavenCentral()
              url 'https://repo1.maven.org/maven2'
          }
      }
      dependencies {
          classpath "com.google.protobuf:protobuf-gradle-plugin:0.8.0"
      }
  }
  
  android {
      compileSdkVersion 23
      buildToolsVersion "23.0.3"
  
      defaultConfig {
          applicationId "com.example.test.testprotobuf"
          minSdkVersion 15
          targetSdkVersion 23
          versionCode 1
          versionName "1.0"
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      compile fileTree(dir: 'libs', include: ['*.jar'])
      testCompile 'junit:junit:4.12'
      compile 'com.android.support:appcompat-v7:23.4.0'
      compile 'com.android.support:design:23.4.0'
  }
  </code></pre>
  
  <p>And gradle-wrapper.properties file:</p>
  
  <pre><code>distributionBase=GRADLE_USER_HOME
  distributionPath=wrapper/dists
  zipStoreBase=GRADLE_USER_HOME
  zipStorePath=wrapper/dists
  distributionUrl=https\://services.gradle.org/distributions/gradle-2.12-all.zip
  </code></pre>
  
  <p>I excute "gradlew build" command successfully. 
  And sync gradle, it prompt that “Error:(2, 0) Cause: org/gradle/api/internal/file/collections/DefaultDirectoryFileTreeFactory
  ” 。</p>