message: Fix Windows installation script error
  Fix an error during Windows installation caused by trying to create the already existing Build directory. Also excluding intermediate steps for Install directory creation.
diff: @@ -48,10 +48,8 @@ CMAKE_CONFIG_GENERATOR="Visual Studio 14 2015 Win64"
  if [ ! -d "$myRepo/opencv" ]; then
  echo "cloning opencv"
  git clone https://github.com/opencv/opencv.git
  - mkdir Build
  - mkdir Build/opencv
  - mkdir Install
  - mkdir Install/opencv
  + mkdir -p Build/opencv
  + mkdir -p Install/opencv
  else
  cd opencv
  git pull --rebase
  @@ -60,8 +58,7 @@ fi
  if [ ! -d "$myRepo/opencv_contrib" ]; then
  echo "cloning opencv_contrib"
  git clone https://github.com/opencv/opencv_contrib.git
  - mkdir Build
  - mkdir Build/opencv_contrib
  + mkdir -p Build/opencv_contrib
  else
  cd opencv_contrib
  git pull --rebase
  