Remove quotes from @extends

[jlsuttles]

These quotes were causing a compile error.

remote: File: /tmp/build_12ac1dd2069443f0bc0592c06b2b24c2/tmp/sass_compiler-input_base_path-6QFAGVDn.tmp/0/typography.scss (24)
remote: ".deluge-font-display4" failed to @extend "".deluge-font-common-base"".
remote: The selector "".deluge-font-common-base"" was not found.
remote: Use "@extend ".deluge-font-common-base" !optional" if the extend should be able to fail.
remote: Error: ".deluge-font-display4" failed to @extend "".deluge-font-common-base"".
remote: The selector "".deluge-font-common-base"" was not found.
remote: Use "@extend ".deluge-font-common-base" !optional" if the extend should be able to fail.
remote:     at options.error (/app/tmp/cache/node_modules/deluge/node_modules/ember-cli-sass/node_modules/broccoli-sass-source-maps/node_modules/node-sass/lib/index.js:272:32)