Making sure travis has the build.txt requirements

.travis.yml

@@ -4,6 +4,7 @@ python:
 
 before_install:
     - make setup
+    - make setup_ci
 
 script:
     - make style

Makefile

@@ -19,6 +19,9 @@ setup:
 	python InvenTree/manage.py migrate --run-syncdb
 	python InvenTree/manage.py check
 
+setup_ci:
+	pip install -U -r requirements/build.txt
+
 develop:
 	pip install -U -r requirements/dev.txt