Call pylint3, not pylint

We use Python 3, so call Pylint for Python 3, not for Python 2.
diff --git a/tests/scripts/check-python-files.sh b/tests/scripts/check-python-files.sh
index a37d1d5..e64d6b3 100755
--- a/tests/scripts/check-python-files.sh
+++ b/tests/scripts/check-python-files.sh
@@ -9,10 +9,10 @@
 # Run 'pylint' on Python files for programming errors and helps enforcing
 # PEP8 coding standards.
 
-if `hash pylint > /dev/null 2>&1`; then
-    pylint -j 2 tests/scripts/generate_test_code.py
-    pylint -j 2 tests/scripts/test_generate_test_code.py
-    pylint -j 2 tests/scripts/mbedtls_test.py
+if `hash pylint3 > /dev/null 2>&1`; then
+    pylint3 -j 2 tests/scripts/generate_test_code.py
+    pylint3 -j 2 tests/scripts/test_generate_test_code.py
+    pylint3 -j 2 tests/scripts/mbedtls_test.py
 else
-    echo "$0: WARNING: 'pylint' not found! Skipping checks on Python files."
+    echo "$0: WARNING: 'pylint3' not found! Skipping checks on Python files."
 fi