[CodeEditor] add min-width for code-area element

This is to prevent textarea getting smaller and smaller for long json
keys.

dist/styles/CodeEditor.css

@@ -24,6 +24,7 @@
 .code-editor .editor .code-area {
   flex-grow: 1;
   max-height: 200px;
+  min-width: 25%;
   overflow: auto;
 }
 .code-editor .editor .code-area .code-container {

dist/styles/CodeEditor.sass

@@ -41,6 +41,7 @@
     .code-area
       flex-grow: 1
       max-height: 200px
+      min-width: 25%
       overflow: auto
       .code-container
         background-color: #fafafa