fixed travis. changed opencv 3.3.0-rc to 3.4

Author: morozovsk

.travis.yml

@@ -45,7 +45,7 @@ install:
   # Download OpenCV v3.3.0-rc
   - git clone https://github.com/opencv/opencv.git
   - cd opencv
-  - git checkout 3.3.0-rc
+  - git checkout 3.4
 
   # Create a new 'build' folder.
   - mkdir build