[ci] simplified and speeded up Travis (#1429)

.travis/setup.sh

@@ -11,11 +11,8 @@ if [[ $TRAVIS_OS_NAME == "osx" ]]; then
 #    brew link --overwrite gcc  # Previous variant to deal with conflict link
     wget -O conda.sh https://repo.continuum.io/miniconda/Miniconda${PYTHON_VERSION:0:1}-latest-MacOSX-x86_64.sh
 else
-    if [[ ${TASK} != "pylint" ]] && [[ ${TASK} != "check-docs" ]]; then
-        sudo add-apt-repository ppa:george-edison55/cmake-3.x -y
-        sudo apt-get update -q
-        sudo apt-get install -y cmake
-        sudo apt-get install -y libopenmpi-dev openmpi-bin build-essential
+    if [[ ${TASK} == "mpi" ]]; then
+        sudo apt-get install -y libopenmpi-dev openmpi-bin
     fi
     wget -O conda.sh https://repo.continuum.io/miniconda/Miniconda${PYTHON_VERSION:0:1}-latest-Linux-x86_64.sh
 fi