Closure Compiler: When building the compiler jar with Maven, specify …

…the exact project to build

BUG=

Review-Url: https://codereview.chromium.org/2133733003
Cr-Commit-Position: refs/heads/master@{#404521}

third_party/closure_compiler/roll_closure_compiler

@@ -47,8 +47,7 @@ EOT
 fi
 
 echo "Building Closure Compiler"
-# TODO(dbeam): can we do less here? As in: build a more specific target.
-mvn install -DskipTests=true
+mvn install -DskipTests=true --projects com.google.javascript:closure-compiler
 
 if [[ "$?" -ne 0 ]]; then
   echo "Failed to build jar, copying nothing" >&2