Fixes last remaining lints and enables scss-lint test for GitLab CI.

With this, builds will now fail if they break the SCSS style guide (at
least, the parts enabled by the linter).

Discussed in #14299.

.csscomb.json

 {
+  "exclude": [
+    "app/assets/stylesheets/framework/tw_bootstrap_variables.scss",
+    "app/assets/stylesheets/framework/fonts.scss"
+  ],
   "always-semicolon": true,
   "color-case": "lower",
   "block-indent": "  ",

.gitlab-ci.yml

@@ -128,7 +128,6 @@ scss-lint:
     - bundle exec rake scss_lint
   tags:
     - ruby
-  allow_failure: true
 
 brakeman:
   stage: test

app/assets/stylesheets/framework/filters.scss

@@ -15,7 +15,7 @@
 @media (max-width: $screen-xs-max) {
   .filter-item {
     display: block;
-    margin: 0 0 10px 0;
+    margin: 0 0 10px;
   }
 }
 

app/assets/stylesheets/framework/fonts.scss

+// Disabling "SpaceAfterPropertyColon" linter because the linter doesn't like
+// the way the `src` property is formatted in this file.
+// scss-lint:disable SpaceAfterPropertyColon
+
 /* latin-ext */
 @font-face {
   font-family: 'Source Sans Pro';

app/assets/stylesheets/framework/nav.scss

@@ -132,7 +132,7 @@
       padding-bottom: 0;
 
       .btn, form, .dropdown, .dropdown-menu-toggle, .form-control {
-        margin: 0 0 10px 0;
+        margin: 0 0 10px;
         display: block;
         width: 100%;
       }

app/assets/stylesheets/notify.scss

@@ -3,12 +3,12 @@ img {
   height: auto;
 }
 p.details {
-  font-style:italic;
-  color:#777
+  font-style: italic;
+  color: #777
 }
 .footer p {
-  font-size:small;
-  color:#777
+  font-size: small;
+  color: #777
 }
 pre.commit-message {
   white-space: pre-wrap;
@@ -20,5 +20,5 @@ pre.commit-message {
   color: #090;
 }
 .file-stats .deleted-file {
-  color: #B00;
+  color: #b00;
 }