Pass verbose flag to rubygems command launching

It makes it much easier to troubleshoot errors.

Author: deivid-rodriguez

gem-maven-plugin/src/main/java/de/saumya/mojo/gem/PackageMojo.java

@@ -181,6 +181,7 @@ public void executeJRuby() throws MojoExecutionException,
                 this.factory.newScriptFromJRubyJar("gem")
                         .addArg("build", this.gemspec)
                         .addArg("--backtrace")
+                        .addArg("--verbose")
                         .executeIn(launchDirectory());
 
                 File newPom = new File( this.gemspec.getParentFile(), "pom." + this.gemspec.getName() + ".xml");
@@ -391,6 +392,7 @@ else if ((Artifact.SCOPE_PROVIDED + Artifact.SCOPE_TEST).contains(dependency.get
         this.factory.newScriptFromJRubyJar("gem")
                 .addArg("build", gemSpec)
                 .addArg("--backtrace")
+                .addArg("--verbose")
                 .executeIn(gemDir);
 
         if ((!localGemspec.exists() || !FileUtils.contentEquals(localGemspec,