update font-face markup and font.scss

the old ```_font.scss``` file had  
```
src: local('Source Sans Pro'), local('SourceSansPro-Regular'), url('../fonts/SourceSansPro-Regular.otf.woff') format('woff2');  
```  
for font files. This caused no font to load in browsers that don't recognize ```woff2``` as a format because a ```woff``` font file was being served with the wrong format.  
example firefox and any browser not google chrome or blink rendering engine :  
![bolt-fontface-update-firefox](https://cloud.githubusercontent.com/assets/5969974/4906125/106b6b32-6456-11e4-9bf7-7cd895bfc4a7.png)  

example chrome (blink engines)  
![chrome-font-face](https://cloud.githubusercontent.com/assets/5969974/4906208/dfe022cc-6456-11e4-8e7b-ca17fe7c9049.png)


The font face syntax is also updated to the newest "bullet proof syntax". ie:  
```
@font-face {
  font-family: 'Source Sans Pro';
  font-style: normal;
  font-weight: 400;
  src: url('../fonts/SourceSansPro-Regular.eot'); /* IE9 Compat Modes */
  src: url('../fonts/SourceSansPro-Regular.eot?#iefix') format('embedded-opentype'), /* IE6-IE8 */
       url('../fonts/SourceSansPro-Regular.woff2') format('woff2'),  /* Serve Woff2 to browsers who accept it fall back to woff below */
       url('../fonts/SourceSansPro-Regular.otf') format('woff'),
       url('../fonts/SourceSansPro-Regular.ttf') format('truetype'); /* Safari, Android, iOS */
}
```  
Now any non chrome / blink browser that doesn't recognize [woff2 - caniuse](http://caniuse.com/#feat=woff2) will receive Source Sans in its headings.  
![bolt-fontface-fixed-firefox](https://cloud.githubusercontent.com/assets/5969974/4906278/83aa0170-6457-11e4-9bef-fc932162a3a5.png)