title: manifestPlaceholders value is not string
body: <p>In my AndroidManifest.xml file I have the following meta-data tag which should be populated dynamically:</p>
  
  <pre><code>&lt;meta-data android:name="com.facebook.sdk.ApplicationId" android:value="${FACEBOOK_APP_ID}"/&gt;
  </code></pre>
  
  <p>My gradle file looks like this:</p>
  
  <pre><code>manifestPlaceholders = [
                  GOOGLE_PROJECT_ID: "A888844613784",
                  FACEBOOK_APP_ID: "888570042741264"
          ]
  </code></pre>
  
  <p>After "Build &amp; Assemble" the FACEBOOK_APP_ID in the manifest file looks like this:</p>
  
  <pre><code> &lt;meta-data
          android:name="com.facebook.sdk.ApplicationId"
          android:value="1481023616.000000" /&gt;
  </code></pre>
  
  <p>Unfortunately this is not a String, but a float value. That's not correct or what I want. </p>
  
  <p>I know there is another way to define the <code>FACEBOOK_APP_ID</code> in the <code>string.xml</code> file. But since I have lots of flavors it would be nice and easy to maintain if we put all flavors-related parameters in the <code>build.gradle</code> file instead of the <code>strings.xml</code> files.</p>
  
  <p>Does anyone know how to avoid the string to float conversion?</p>