[skip appveyor] -y flag for repo add

Author: skvark

.travis.yml

@@ -15,9 +15,8 @@ before_install:
 
 install: 
   - sudo apt-get install cmake
-  - sudo add-apt-repository ppa:fkrull/deadsnakes
-  - if [[ $TRAVIS_PYTHON_VERSION == 2* ]]; then sudo apt-get install python2.7-dev; fi
-  - if [[ $TRAVIS_PYTHON_VERSION == 3* ]]; then sudo apt-get install python3.5-dev; fi
+  - if [[ $TRAVIS_PYTHON_VERSION == 3* ]]; then sudo add-apt-repository ppa:fkrull/deadsnakes -y; fi
+  - if [[ $TRAVIS_PYTHON_VERSION == 3* ]]; then sudo apt-get install libpython3.5-dev; fi
   - python -m pip install --upgrade pip
   - pip install -r requirements.txt
   - cd opencv