title: protobuf maven 3 protoc plugin error
body: <p>in my pom.xml I have following google protobuf plugin declaration:</p>
  
  <pre><code>&lt;plugin&gt;
              &lt;groupId&gt;com.google.protobuf.tools&lt;/groupId&gt;
              &lt;artifactId&gt;maven-protoc-plugin&lt;/artifactId&gt;
              &lt;version&gt;0.3.1&lt;/version&gt;
  
              &lt;configuration&gt;
                  &lt;protocExecutable&gt;protoc&lt;/protocExecutable&gt;
                  &lt;protoSourceRoot&gt;${project.basedir}/src/main/protobuf/&lt;/protoSourceRoot&gt;
                  &lt;languageSpecifications&gt;
                      &lt;LanguageSpecification&gt;
                          &lt;language&gt;JAVA&lt;/language&gt;
                          &lt;outputDirectory&gt;${project.basedir}/src/main/java&lt;/outputDirectory&gt;
                      &lt;/LanguageSpecification&gt;
                  &lt;/languageSpecifications&gt;
              &lt;/configuration&gt;
              &lt;executions&gt;
                  &lt;execution&gt;
                      &lt;goals&gt;
                          &lt;goal&gt;compile&lt;/goal&gt;
                      &lt;/goals&gt;
                  &lt;/execution&gt;
              &lt;/executions&gt;
          &lt;/plugin&gt;
  </code></pre>
  
  <p>but my eclipse shows following error:</p>
  
  <pre><code>protoc did not exit cleanly. Review output for more information. (com.google.protobuf.tools:maven-protoc-plugin:0.3.1:compile:default:generate-sources)
  </code></pre>
  
  <p>How to solve this ? Thanks</p>