Added Angular as a dependency to the Bower config

It is common for front-end build tools to concatenate 3rd party JS libs together into a single file. Various tools (such as Gulp with the gulp-bower-files plugin) rely on the dependencies in a library's `bower.json` file to concatenate these files in the correct order.

Without specifying Angular itself as a dependency the angular-truncate module can end up appearing before Angular itself, which obviously breaks.

This pull request simply adds Angular as a dependency. I've specified 1.2.0 as the base version but I haven't tested this module with earlier versions. You may want to change the listed version number as necessary.