Enable parallel build in appveyor

Author: paceholder

.appveyor.yml

@@ -1,3 +1,5 @@
+clone_depth: 5
+
 environment:
   QTDIR32: C:\Qt\5.7\msvc2015
   QTDIR64: C:\Qt\5.7\msvc2015_64
@@ -20,6 +22,7 @@ before_build:
   - cmd: if "%platform%"=="x64"   cmake "-G%GENERATOR64%" -DCMAKE_PREFIX_PATH="%QTDIR64%/lib/cmake/Qt5" ..
 
 build:
+  parallel: true
   project: C:\projects\nodeeditor\build\NodeEditor.sln
 
 #build_script: