fixed typo in scope_method.cson

there is a typo in `scope_method.cson` - the PR should fix it

this is the message in dev tools:

    Error reading snippets file '/Users/username/.atom/packages/angularjs-snippets/snippets/scope_method.cson': [stdin]:1:15: error: unexpected :
    ``'.source.js':
                  ^ /Applications/Atom.app/Contents/Resources/app/node_modules/snippets/lib/snippets.js:132