fixing pytest call

.travis.yml

@@ -5,7 +5,6 @@ sudo: required
 
 before_script:
   - export PATH=/usr/bin:$PATH
-  - pip install -U pytest
   - sudo apt-get update -qq
   - sudo apt-get install -yq python-dev python-numpy python-opencv
   - sudo ln /dev/null /dev/raw1394
@@ -38,5 +37,6 @@ install:
 
 script:
   - uname -a
+  - pytest --version
   - python -m pytest --version
   - make test
\ No newline at end of file

Makefile

 install:
-	pip install -r requirements.txt
+	pip install -U -r requirements.txt
 
 test:
 	python -m pytest tests/

requirements.txt

+pytest
 sphinx
 numpy