Use V2 of RTD's configuration file (#2418)

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

.readthedocs.yml

@@ -1,3 +1,5 @@
+version: 2
+
 formats:
   - pdf
 
@@ -6,7 +8,10 @@ build:
 
 python:
   version: 3.7
-  pip_install: true
-  extra_requirements:
-    - docs
-    - mongo
+  install:
+    - requirements: docs/requirements.txt
+    - method: pip
+      path: .
+      extra_requirements:
+        - docs
+        - mongo

docs/requirements.txt

@@ -0,0 +1,2 @@
+# We still need this because RTD is special
+setuptools==40.8.0