Version 5.1.0

Changes:
- Removes compatibility with pre-release `poetry`. (Minor version bump.)
- Bump `werkzeug` version to address security issue.
- Correct word splitting on `pip` commands.
- circle CI is working again; much thanks to @miketheman

Known risks:
- Windows CI is still down

package.json

@@ -1,6 +1,6 @@
 {
   "name": "serverless-python-requirements",
-  "version": "5.0.1",
+  "version": "5.1.0",
   "engines": {
     "node": ">=10.0"
   },