Fix test for files with non ASCII characters

The previous check was to general since it catched also files were non ASCII
characters are allowed (e.g. Latex files).
Now test only for source code files and check for files which are of
non ASCII type.

scripts/check-non-ascii-characters.sh

@@ -20,9 +20,12 @@ fi
 echo "Upstream name is :" $UPSTREAM
 
 BASE_COMMIT=$UPSTREAM/master
-CHANGED_FILES=$(git diff --name-only $BASE_COMMIT)
+# check only source code files
+CHANGED_FILES=$(git diff --name-only $BASE_COMMIT | grep -E '.*\.(h|hpp|c|C|cpp|cxx|tpl)$' | grep -viE '.*LinkDef.h$')
+
 for file in $CHANGED_FILES; do
-  result=$(file $file | grep UTF-8)
+  # find all source code files which are non ASCII ones
+  result=$(file $file | grep -v ASCII)
   if [[ "$result" != "" ]]; then
     echo " "
     echo "File $file contains non ASCII characters"