minor #8030 Fix and align travis and platform build environments (robfrawley)

This PR was merged into the 2.7 branch.

Discussion
----------

Fix and align travis and platform build environments

This pull request fixes the `platform.sh` deploy and aligns the `platform.sh` and `travis-ci.org` build to use the same version constraints and environments. Per @xabbuh in #8009 (comment) this PR has been made against the `2.7` branch. Original implementation pulled from #8010 and #8009. Changes include:

- Update the `pip` version requirements pulled in by [_build/.requirements.txt](https://github.com/robfrawley/symfony-docs/blob/feature-align-travis-and-platform-build/_build/.requirements.txt) to latest releases, except for `sphinx` which must be downgraded to `1.3` until we find a solution for `sphinx-php` (which there doesn't seem to be much interest in fixing: #7402 (comment), #7422, fabpot/sphinx-php#33).

- Use the same package management and constraint requirements for both `platform.sh` and `travis-ci.org` by having both utilize the `_build/.requirements.txt` file when calling `pip`.

- Use the same documentation build command to compile the documentation HTML (`make`) while still calling `sphinx` with "strict mode" (or, more accurately, "turn warnings into errors mode") for `travis-ci.org`.

- On `platform.sh`, since the `vitrualenv` folder is at the documentation root, remove all `rst` files contained within it (pulled in from the `pip` packages) via a `find` command, so as to ensure the build doesn't pull them in (they would never appear in the output as they don't exist in the doctree, but if they contain errors or other inconsistencies, this could cause the build to fail while reading in their sources).
  - `find .virtualenv -type f -name "*.rst" -delete`

Commits
-------

764bc37 align travis and platform build environments

Author: weaverryan

.platform.app.yaml

@@ -57,4 +57,5 @@ hooks:
       export PIP_USER=
       pip install pip==9.0.1 wheel==0.29.0
       pip install -r _build/.requirements.txt
+      find .virtualenv -type f -name "*.rst" -delete
       make -C _build html

.travis.yml

@@ -6,9 +6,9 @@ sudo: false
 cache:
   directories: [$HOME/.cache/pip]
 
-install: pip install sphinx~=1.3.0 git+https://github.com/fabpot/sphinx-php.git
+install: pip install -r _build/.requirements.txt
 
-script: sphinx-build -nW -c _build/ -b html -d _build/doctrees . _build/html
+script: make -C _build SPHINXOPTS=-nW html
 
 branches:
   except:

_build/.requirements.txt

@@ -1,14 +1,13 @@
-alabaster==0.7.9
-Babel==2.3.4
+alabaster==0.7.10
+Babel==2.4.0
 docutils==0.13.1
 imagesize==0.7.1
-Jinja2==2.9.4
-MarkupSafe==0.23
+Jinja2==2.9.6
+MarkupSafe==1.0
 Pygments==2.2.0
-pytz==2016.10
+pytz==2017.2
 requests==2.12.5
 six==1.10.0
 snowballstemmer==1.2.1
-Sphinx==1.5.2
+Sphinx==1.3.6
 git+https://github.com/fabpot/sphinx-php.git@7312eccce9465640752e51373a480da700e02345#egg_name=sphinx-php
-