Update docs.yml

Author: jph00

.github/workflows/docs.yml

@@ -21,6 +21,7 @@ jobs:
     container: fastai/fastai
     steps:
     - uses: actions/checkout@v2
+    - uses: fastai/workflows/conda-env@master
     - uses: fastai/workflows/build-docs@master
       with:
         username: jeremyphoward