Install ourselves in dev-requirements.txt, not just travis.ci

Otherwise RTD always pulls from PyPI instead of self.

Author: bitprophet

.travis.yml

@@ -31,8 +31,5 @@ install:
 script:
   - inv travis.blacken
   - flake8
-  # We have no real tests at present so we just make sure installation works,
-  # first off.
-  - pip install .
   # Does our own dogfooding website build ok? :D
   - inv docs

dev-requirements.txt

@@ -6,3 +6,7 @@ wheel==0.24
 twine==1.11.0
 releases>=1.5.1,<2.0
 flake8==2.4.0
+
+# Install ourselves direct, even when being used on eg RTD. Otherwise we can't
+# dogfood our own changes until release to PyPI.
+-e .