Examples: Ignore all *.user files (#1919)

For example `Qt Creator` create `CMakeLists.txt.user` file with user settings.

examples/.gitignore

@@ -6,7 +6,7 @@ build/*
 *.opensdf
 *.sdf
 *.suo
-*.vcxproj.user
+*.user
 *.o
 *.obj
 *.exe