fix high cpu usage issue that occured in Firefox

fixes issue related with #342 (Merge Request view causes 100% CPU in firefox)

CHANGELOG

@@ -7,6 +7,7 @@ v 7.1.0
   - Add @all mention for comments
   - Dont show reply button if user is not signed in
   - Expose more information for issues with webhook
+  - Fix cpu usage issue in Firefox
 v 7.0.0
   - The CPU no longer overheats when you hold down the spacebar

app/assets/javascripts/markdown_area.js.coffee

@@ -20,6 +20,9 @@ $(document).ready ->
   $(".div-dropzone-hover").append iconPicture
   $(".div-dropzone").append divSpinner 
   $(".div-dropzone-spinner").append iconSpinner
+  $(".div-dropzone-spinner").css
+    "opacity": 0
+    "display": "none"
   dropzone = $(".div-dropzone").dropzone(
     url: project_image_path_upload
@@ -66,13 +69,17 @@ $(document).ready ->
       return
     sending: ->
-      $(".div-dropzone-spinner").css "opacity", 0.7
+      $(".div-dropzone-spinner").css
+        "opacity": 0.7
+        "display": "inherit"
       return
     complete: ->
       $(".dz-preview").remove()
       $(".markdown-area").trigger "input"
-      $(".div-dropzone-spinner").css "opacity", 0
+      $(".div-dropzone-spinner").css
+        "opacity": 0
+        "display": "none"
       return
   )
@@ -163,10 +170,14 @@ $(document).ready ->
       val + url + "\n"
   showSpinner = (e) ->
-    $(".div-dropzone-spinner").css "opacity", 0.7
+    $(".div-dropzone-spinner").css
+      "opacity": 0.7
+      "display": "inherit"
   closeSpinner = ->
-    $(".div-dropzone-spinner").css "opacity", 0
+    $(".div-dropzone-spinner").css
+      "opacity": 0
+      "display": "none"
   showError = (message) ->
     checkIfMsgExists = $(".error-alert").children().length