Move packages to requirementwqs file

Author: OskarStark

.symfony.cloud.yaml

@@ -52,7 +52,6 @@ hooks:
       . .virtualenv/bin/activate
       # SymfonyCloud currently sets PIP_USER=1.
       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

_build/.requirements.txt

@@ -1,3 +1,5 @@
+pip==9.0.1
+wheel==0.29.0
 alabaster==0.7.10
 Babel==2.4.0
 docutils==0.13.1