Replaces usages of .mini selector with [mini]

static/panels.less

@@ -99,7 +99,7 @@ atom-panel[location="modal"] {
     font-size: 1.3em;
   }
 
-  atom-text-editor.mini {
+  atom-text-editor[mini] {
     margin-bottom: 10px;
   }
 

static/text-editor-light.less

@@ -8,7 +8,7 @@ atom-text-editor {
   line-height: 1.3;
 }
 
-atom-text-editor.mini {
+atom-text-editor[mini] {
   font-size: @input-font-size;
   line-height: @component-line-height;
   max-height: @component-line-height + 2; // +2 for borders