Update readthedocs to use pip

Author: alejandrogallo

readthedocs.yml .readthedocs.ymlreadthedocs.yml renamed to .readthedocs.yml

@@ -1,11 +1,11 @@
-formats:
-    - none
 build:
     image: latest
 python:
    version: 3.6
    # Note that pip_install is buggy, but setup_py_install will not take into
    # account any dependencies from setup.py. *All* dependencies must be
    # declared in docs/rtd_environment.yml
-   setup_py_install: true
-   pip_install: false
+   #setup_py_install: true
+   pip_install: true
+   extra_requirements:
+     - dev