Added cache again

.travis.yml

@@ -3,11 +3,16 @@ os: linux
 dist: trusty
 compiler: gcc
 
+cache:
+  directories:
+    - qt5
+
 before_script:
-  - git clone --branch=5.10 git://code.qt.io/qt/qt5.git
+  - mkdir -p qt5
+  - if [ ! -d qt5/.git ] ; then rm qt5 -Rf ; git clone --branch=5.10 git://code.qt.io/qt/qt5.git ; fi
   - pushd qt5
-  - perl init-repository --module-subset=qtbase,qtimageformats
-  - ./configure -opensource -nomake examples -nomake tests -confirm-license
+  - if [ ! -d qtbase/.git ] ; then perl init-repository --module-subset=qtbase,qtimageformats ; fi
+  - if [ ! -f config.summaryr ] ; then ./configure -opensource -nomake examples -nomake tests -confirm-license ; fi
   - make -j2
   - sudo make install
   - popd