Rakefile : add logic if compiler isn't there

Rakefile

@@ -2,19 +2,22 @@
 # 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
-  puts "Minifying jquery.isotope.js..."
-  sh "java -jar #{compiler} --js #{js} --js_output_file #{min_js}"
-  # Adds header comment
-  min = File.read( min_js )
-  File.open( min_js, 'w') do |f|
-    f.write File.readlines( js )[0..9].join()
-    f.write min
+  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
+    min = File.read( min_js )
+    File.open( min_js, 'w') do |f|
+      f.write File.readlines( js )[0..9].join()
+      f.write min
+    end
   end
-end
-
+end