UI: Add missing override specifier

Found via clang-3.6, actual warning:
window-basic-main.hpp:406:14: warning: 'GetProfilePath' overrides
a member function but is not marked 'override'
[-Winconsistent-missing-override]

obs/window-basic-main.hpp

@@ -404,7 +404,7 @@ public:
 	virtual config_t *Config() const override;
 
 	virtual int GetProfilePath(char *path, size_t size, const char *file)
-		const;
+		const override;
 
 private:
 	std::unique_ptr<Ui::OBSBasic> ui;