BUG: Fix invalid environment file (#345)

(Picked up by `pre-commit`).

Online validator: https://codebeautify.org/yaml-validator/y22f4ba39

new_project_template/environment.yml

@@ -5,5 +5,5 @@ channels:
 dependencies:
   - pip=20.1.1
   - python=3.7.3
-  pip:
+  - pip:
     - pytest==6.2.2