Delete bower install from README.md (#725)

As Bower is deprecated a long time ago: https://bower.io/blog/2017/how-to-migrate-away-from-bower/

It does't make sense to mention it in the readme.

README.md

@@ -29,11 +29,6 @@ You can get Mustache via [npm](http://npmjs.com).
 ```bash
 $ npm install mustache --save
 ```
-or install with bower:
-
-```bash
-$ bower install --save mustache
-```
 
 ## Command line tool