travis: better pip usage

.gitignore

@@ -4,20 +4,18 @@
 .project
 .pydevproject
 
-# coverage generated:
+# coverage generated
 /cover-html/
 .coverage
 .coveralls.yml
 
-# Compiled source #
-###################
+# Compiled source
 *.pyc
 *.py~
 *.pyproj
 *.sln
 
-# Headphones files #
-######################
+# Headphones files
 *.log
 *.db*
 *.db-journal
@@ -26,27 +24,25 @@ version.lock
 logs/*
 cache/*
 
-# HTTPS Cert/Key #
-##################
+# HTTPS Cert/Key
 *.crt
 *.key
 *.csr
 
-# OS generated files #
-######################
+# OS generated files
 .DS_Store?
 .DS_Store
 ehthumbs.db
 Icon?
 Thumbs.db
 
-#Ignore files generated by PyCharm
+# Ignore files generated by PyCharm
 .idea/*
 
-#Ignore files generated by vi
+# Ignore files generated by vi
 *.swp
 
-#Ignore files build by Visual Studio
+# Ignore files build by Visual Studio
 *.obj
 *.exe
 *.pdb
@@ -72,3 +68,6 @@ obj/
 [Rr]elease*/
 _ReSharper*/
 .vscode
+
+# Python virtual env
+venv