Rename .scss files to use snake_case

See https://gitlab.com/gitlab-org/gitlab-ce/issues/42908

app/assets/stylesheets/framework.scss

@@ -21,7 +21,7 @@
 @import "framework/flash";
 @import "framework/forms";
 @import "framework/gfm";
-@import "framework/gitlab-theme";
+@import "framework/gitlab_theme";
 @import "framework/header";
 @import "framework/highlight";
 @import "framework/issue_box";
@@ -35,10 +35,10 @@
 @import "framework/pagination";
 @import "framework/panels";
 @import "framework/popup";
-@import "framework/secondary-navigation-elements";
+@import "framework/secondary_navigation_elements";
 @import "framework/selects";
 @import "framework/sidebar";
-@import "framework/contextual-sidebar";
+@import "framework/contextual_sidebar";
 @import "framework/tables";
 @import "framework/notes";
 @import "framework/tabs";
@@ -49,16 +49,16 @@
 @import "framework/zen";
 @import "framework/blank";
 @import "framework/wells";
-@import "framework/page-header";
+@import "framework/page_header";
 @import "framework/awards";
 @import "framework/images";
-@import "framework/broadcast-messages";
+@import "framework/broadcast_messages";
 @import "framework/emojis";
-@import "framework/emoji-sprites";
+@import "framework/emoji_sprites";
 @import "framework/icons";
 @import "framework/snippets";
 @import "framework/memory_graph";
 @import "framework/responsive_tables";
-@import "framework/stacked-progress-bar";
+@import "framework/stacked_progress_bar";
 @import "framework/ci_variable_list";
 @import "framework/feature_highlight";

lib/tasks/gemojione.rake

@@ -115,7 +115,7 @@ namespace :gemojione do
         end
       end
 
-      style_path = Rails.root.join(*%w(app assets stylesheets framework emoji-sprites.scss))
+      style_path = Rails.root.join(*%w(app assets stylesheets framework emoji_sprites.scss))
 
       # Combine the resized assets into a packed sprite and re-generate the SCSS
       SpriteFactory.cssurl = "image-url('$IMAGE')"