Rakefile : add logic if compiler isn't there

Rakefile

@@ -2,12 +2,15 @@
 # requires Google Closure Compiler http://code.google.com/closure/compiler/
 # from command line run:
 #     rake min COMPILER='path/to/compiler.jar'
-file compiler = ENV["COMPILER"] || '~/resources/google-closure/compiler.jar'
+file compiler = ENV["COMPILER"] || '../../resources/google-closure/compiler.jar'
 js = 'jquery.isotope.js'
 min_js = 'jquery.isotope.min.js'
 
 desc "Generates #{min_js}"
 task :min do
+  unless File.exists?( compiler )
+    puts "ERROR: Compiler not found at " + compiler
+  else
     puts "Minifying jquery.isotope.js..."
     sh "java -jar #{compiler} --js #{js} --js_output_file #{min_js}"
     # Adds header comment
@@ -17,4 +20,4 @@ task :min do
       f.write min
     end
   end
-
+end