title: Error running PuppyCrawl's Maven Checkstyle Plugin
body: <p>Well, I'm trying to configure Maven's Checkstyle Plugin on the project I'm currently working on and I'm getting the following:</p>
  
  <pre><code>[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:3.0.0:check (verify-style) on project email: Failed during checkstyle execution: Failed during checkstyle configuration: unable to parse configuration stream: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target -&gt; [Help 1]
  </code></pre>
  
  <p>So, running <code>mvn install -X</code> I've got the following stacktrace: </p>
  
  <pre><code>Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
          at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:387)
          at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
          at sun.security.validator.Validator.validate(Validator.java:260)
          at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:324)
          at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:229)
          at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:124)
          at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1491)
          ... 52 more
  Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
          at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
          at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
          at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
          at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:382)
          ... 58 more
  </code></pre>
  
  <p>It seems to be related to the DTD specified on the google-checks.xml I've found on the following link on Github: <a href="https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml" rel="nofollow noreferrer">https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml</a>:</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;!DOCTYPE module PUBLIC
            "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
            "https://checkstyle.org/dtds/configuration_1_3.dtd"&gt;
  </code></pre>
  
  <p>I've tried to add that certificate to my JVM truststore but it doesn't work.
  Can anybody figure out what's going wrong?</p>
  
  <p>Thank you in advance. </p>