use VERSION file and set dev version

.github/workflows/pypi.yml

@@ -48,9 +48,9 @@ jobs:
         id: tag
         run: echo ::set-output name=TAG_NAME::$(echo $GITHUB_REF | cut -d / -f 3)
 
-      - name: Update version in setup.py
+      - name: Update version in src/axolotl/__init__.py
         run: |
-          sed -i -E 's/version="([0-9.]+)",/version="${{ steps.tag.outputs.TAG_NAME }}",/g' setup.py
+          sed -i -E's/__version__ = "([0-9.]+)"/__version__ = "${{ steps.tag.outputs.TAG_NAME }}"/g' src/axolotl/__init__.py
 
       - name: Build a source dist
         run: |