Fixed #2. No need to verify that a file exists

Under gulp, there is no need to check that a file exists. Additionally, there is actually a high likelihood that the file *doesn't* exist, such as when a set of Jade or Handlebars templates is loaded up, preprocessed into HTML, and then passed into `gulp-html2js`. The intermediate files are never written, unlike Grunt where they must be.

This fix eliminates all of the File Exists checks, relying entirely on `gulp` and `file.contents` from the gulp stream. This allows steps to exist earlier in the pipe stream, such as Jade or Handlebars processing.