use an array to get mirahc in the gem closes #278

the gemspec is loaded when rake is loaded, and at that point the dist file isn't created. Dir::[] returns an empty array if nothing matches, so the first gem call will fail. This fixes that

mirah.gemspec

@@ -3,7 +3,7 @@ $: << './lib'
 require 'mirah/version'
 
 files = Dir["{bin,lib,test,examples}/**/*"] \
-        + Dir['dist/mirahc.jar']            \
+        + ['dist/mirahc.jar']               \
         + Dir["{*.md,*.txt,Rakefile}"]      \
         - Dir["{examples/wiki/**/*}"]