Avoid removing vital build/ directory in prepublish script.

I'm sure this isn't the best way to fix this problem, but without it the
pathwatcher package gets installed without a build/Release directory,
which makes the package totally unusable. The unnecessary cleaning happens
because the prepublish script always runs after npm install.

Very open to any other ways of preserving the build/ directory!

Gruntfile.coffee

@@ -69,7 +69,7 @@ module.exports = (grunt) ->
   grunt.registerTask('lint', ['coffeelint', 'cpplint'])
   grunt.registerTask('default', ['coffee', 'lint', 'shell:rebuild'])
   grunt.registerTask('test', ['default', 'shell:test'])
-  grunt.registerTask('prepublish', ['clean', 'coffee', 'lint', 'shell:update-atomdoc', 'atomdoc'])
+  grunt.registerTask('prepublish', ['coffee', 'lint', 'shell:update-atomdoc', 'atomdoc'])
   grunt.registerTask 'clean', ->
     rm = require('rimraf').sync
     rm 'build'