Check docs (#509)

* Require HTML docs to build cleanly for Travis

.travis.yml

@@ -19,10 +19,12 @@ install:
   - pip install ecdsa
   - pip install plyvel
   - pip install pycodestyle
+  - pip install pylru
   - pip install pyrocksdb
-  - pip install tribus-hash
   - pip install pytest-cov
-  - pip install pylru
+  - pip install Sphinx
+# hashes
+  - pip install tribus-hash
   - pip install blake256
   - pip install x11_hash
   - pip install xevan_hash
@@ -32,6 +34,7 @@ install:
 script:
   - pytest --cov=server --cov=lib --cov=wallet
   - pycodestyle server/*.py lib/*.py
+  - sh -c "cd docs && make html"
 # Dont report coverage from nightly
 after_success:
   - if [[ $(python3 -V 2>&1) == *"Python 3.6"* ]]; then

docs/Makefile

@@ -2,7 +2,7 @@
 #
 
 # You can set these variables from the command line.
-SPHINXOPTS    =
+SPHINXOPTS    = -W
 SPHINXBUILD   = sphinx-build
 SPHINXPROJ    = ElectrumX
 SOURCEDIR     = .