Modified javascript build instructions and build to use the maven build

for closure compiler: newer versions of the compiler have stopped ant
build support.

javascript/README.md

@@ -33,7 +33,7 @@ If you don't checkout the dependencies next to libphonenumber:
 How to compile:
 ===============
 1. Build Closure's compiler.jar:
-  `ant -f ~/src/closure-compiler/build.xml`
+  `mvn -DskipTests`
 
 2. Compile the demo.js and all its dependencies to one file: `demo-compiled.js`:
   `ant -f javascript/build.xml compile-demo`

javascript/build.xml

@@ -4,7 +4,7 @@
   <property name="closure-compiler.dir"
             value="${basedir}/../../closure-compiler" />
   <property name="closure-compiler.jar"
-            value="${closure-compiler.dir}/build/compiler.jar" /> 
+            value="${closure-compiler.dir}/target/closure-compiler-1.0-SNAPSHOT.jar" /> 
   <property name="closure-library.dir"
             value="${basedir}/../../closure-library" />
   <property name="closure-linter.dir"