BLD: add trailing-whitespace pre-commit hook

Author: plammens

.pre-commit-config.yaml

@@ -62,3 +62,4 @@ repos:
     hooks:
     -   id: end-of-file-fixer
         exclude: '.html$|^LICENSES/|.csv$|.txt$|.svg$|.py$'
+    -   id: trailing-whitespace