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

For example `Qt Creator` create `CMakeLists.txt.user` file with user settings.
diff --git a/examples/.gitignore b/examples/.gitignore
index 33f184b..d5786ab 100644
--- a/examples/.gitignore
+++ b/examples/.gitignore
@@ -6,7 +6,7 @@
 *.opensdf
 *.sdf
 *.suo
-*.vcxproj.user
+*.user
 *.o
 *.obj
 *.exe