[Tests] Tighten up doc testing

.travis.yml

@@ -6,7 +6,7 @@ python:
   - 3.3
   - 3.4
   - 3.5
-  - "3.6-dev"
+  - "nightly"
   - "pypy"
   - "pypy3"
 env:
@@ -16,7 +16,7 @@ matrix:
   allow_failures:
     - python: 2.7
     - python: "pypy"
-    - python: "3.6-dev"
+    - python: "nightly"
     - env: DOC_TESTS=true
   fast_finish: true
   exclude:
@@ -37,8 +37,8 @@ before_install:
 # command to install dependencies
 install:
   - pip install --upgrade pip
-  - pip install -r requirements.txt
   - if [ "$UNIT_TESTS" = "true" ]; then
+      pip install -r requirements.txt;
       pip install -r tests/requirements.txt;
       pip install coveralls;
     fi
@@ -61,7 +61,11 @@ script:
     fi
   - if [ "$DOC_TESTS" = "true" ]; then
       isort --recursive colourettu --verbose;
+    fi
+  - if [ "$DOC_TESTS" = "true" ]; then
       pydocstyle colourettu;
+    fi
+  - if [ "$DOC_TESTS" = "true" ]; then
       pycodestyle colourettu;
     fi
 after_success: