Remove protocol in Tiny MCE’s font URLs

Allow the fonts to be served using the same protocol as the current
page.

common/static/css/tiny-mce.css

-@font-face{font-family:'Open Sans';font-style:normal;font-weight:700;src:local("Open Sans Bold"),local("OpenSans-Bold"),url(http://themes.googleusercontent.com/static/fonts/opensans/v6/k3k702ZOKiLJc3WVjuplzKRDOzjiPcYnFooOUGCOsRk.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:normal;font-weight:300;src:local("Open Sans Light"),local("OpenSans-Light"),url(http://themes.googleusercontent.com/static/fonts/opensans/v6/DXI1ORHCpsQm3Vp6mXoaTaRDOzjiPcYnFooOUGCOsRk.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:italic;font-weight:700;src:local("Open Sans Bold Italic"),local("OpenSans-BoldItalic"),url(http://themes.googleusercontent.com/static/fonts/opensans/v6/PRmiXeptR36kaC0GEAetxhbnBKKEOwRKgsHDreGcocg.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:italic;font-weight:300;src:local("Open Sans Light Italic"),local("OpenSansLight-Italic"),url(http://themes.googleusercontent.com/static/fonts/opensans/v6/PRmiXeptR36kaC0GEAetxvR_54zmj3SbGZQh3vCOwvY.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:italic;font-weight:400;src:local("Open Sans Italic"),local("OpenSans-Italic"),url(http://themes.googleusercontent.com/static/fonts/opensans/v6/xjAJXh38I15wypJXxuGMBrrIa-7acMAeDBVuclsi6Gc.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:normal;font-weight:400;src:local("Open Sans"),local("OpenSans"),url(http://themes.googleusercontent.com/static/fonts/opensans/v6/cJZKeOuBrn4kERxqtaUH3bO3LdcAZYWl9Si6vvxL-qU.woff) format("woff")}
+@font-face{font-family:'Open Sans';font-style:normal;font-weight:700;src:local("Open Sans Bold"),local("OpenSans-Bold"),url(//themes.googleusercontent.com/static/fonts/opensans/v6/k3k702ZOKiLJc3WVjuplzKRDOzjiPcYnFooOUGCOsRk.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:normal;font-weight:300;src:local("Open Sans Light"),local("OpenSans-Light"),url(//themes.googleusercontent.com/static/fonts/opensans/v6/DXI1ORHCpsQm3Vp6mXoaTaRDOzjiPcYnFooOUGCOsRk.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:italic;font-weight:700;src:local("Open Sans Bold Italic"),local("OpenSans-BoldItalic"),url(//themes.googleusercontent.com/static/fonts/opensans/v6/PRmiXeptR36kaC0GEAetxhbnBKKEOwRKgsHDreGcocg.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:italic;font-weight:300;src:local("Open Sans Light Italic"),local("OpenSansLight-Italic"),url(//themes.googleusercontent.com/static/fonts/opensans/v6/PRmiXeptR36kaC0GEAetxvR_54zmj3SbGZQh3vCOwvY.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:italic;font-weight:400;src:local("Open Sans Italic"),local("OpenSans-Italic"),url(//themes.googleusercontent.com/static/fonts/opensans/v6/xjAJXh38I15wypJXxuGMBrrIa-7acMAeDBVuclsi6Gc.woff) format("woff")}@font-face{font-family:'Open Sans';font-style:normal;font-weight:400;src:local("Open Sans"),local("OpenSans"),url(//themes.googleusercontent.com/static/fonts/opensans/v6/cJZKeOuBrn4kERxqtaUH3bO3LdcAZYWl9Si6vvxL-qU.woff) format("woff")}
 
 .mceContentBody {
     padding: 10px;