add pre-commit and enforce on travis (#37)

* add pre-commit and enforce on travis

.pre-commit-config.yaml

@@ -0,0 +1,19 @@
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.3.0
+    hooks:
+    -   id: check-added-large-files
+    -   id: check-ast
+    -   id: check-case-conflict
+    -   id: check-json
+    -   id: check-merge-conflict
+    -   id: check-yaml
+    -   id: debug-statements
+    -   id: detect-aws-credentials
+        args: [--allow-missing-credentials]
+    -   id: detect-private-key
+    -   id: end-of-file-fixer
+    -   id: pretty-format-json
+        args: [--autofix]
+    -   id: requirements-txt-fixer
+    -   id: trailing-whitespace