Fix final warning in Xcode 10 and add .DS_Store to .gitignore to please Mac developers (#86)

.gitignore

@@ -3,3 +3,4 @@ Bonzomatic
 tmp
 build
 .vs
+.DS_Store

src/ShaderEditor.cpp

@@ -80,7 +80,7 @@ public:
 static unsigned int wndID = 1;
 void ShaderEditor::Initialise()
 {
-  wMain = (Scintilla::WindowID)(wndID++);
+  wMain = (Scintilla::WindowID)(unsigned long)(wndID++);
 
   lexState = new Scintilla::LexState( pdoc );