update travis.yml for gfortran 5.1

Author: jacobwilliams

.travis.yml

@@ -53,10 +53,10 @@ install:
       mkdir "$HOME/.local/bin"
     fi
   - export PATH="$HOME/.local/bin:$PATH"
-  - export FC=/usr/bin/gfortran-4.9
-  - ln -fs /usr/bin/gfortran-4.9 "$HOME/.local/bin/gfortran" && gfortran --version
-  - ls -l /usr/bin/gfortran-4.9
-  - ln -fs /usr/bin/gcov-4.9 "$HOME/.local/bin/gcov" && gcov --version
+  - export FC=/usr/bin/gfortran-5.1
+  - ln -fs /usr/bin/gfortran-5.1 "$HOME/.local/bin/gfortran" && gfortran --version
+  - ls -l /usr/bin/gfortran-5.1
+  - ln -fs /usr/bin/gcov-5.1 "$HOME/.local/bin/gcov" && gcov --version
   - |
     if ! which f90split; then
       wget http://people.sc.fsu.edu/~jburkardt/f_src/f90split/f90split.f90 && \