chore(Rakefile): tune JVM for closure compiler

Using the client VM and forcing 32bit mode gives us huge perf boost.

before:

reali   0m8.173s
user    0m39.984s
sys     0m1.408s

after:

real    0m3.000s
user    0m12.687s
sys     0m0.852s

Rakefile

@@ -290,7 +290,10 @@ def closure_compile(filename)
 
   min_path = path_to(filename.gsub(/\.js$/, '.min.js'))
 
-  %x(java -jar lib/closure-compiler/compiler.jar \
+  %x(java \
+        -client \
+        -d32 \
+        -jar lib/closure-compiler/compiler.jar \
         --compilation_level SIMPLE_OPTIMIZATIONS \
         --language_in ECMASCRIPT5_STRICT \
         --js #{path_to(filename)} \