Fix the build constraints syntax for appengine

colorable_others.go

@@ -1,4 +1,4 @@
-// +build !windows OR appengine
+// +build !windows appengine
 
 package colorable
 

colorable_windows.go

@@ -1,3 +1,4 @@
+// +build windows
 // +build !appengine
 
 package colorable