Update to gcc 4.9 for Travis CI runs

.travis.yml

@@ -7,10 +7,14 @@ python:
   - "3.6"
 addons:
   apt:
+    sources:
+      - ubuntu-toolchain-r-test
     packages:
-    - gfortran
-    - mpich
-    - libmpich-dev
+      - gcc-4.9
+      - g++-4.9
+      - gfortran-4.9
+      - mpich
+      - libmpich-dev
 cache:
   directories:
   - $HOME/nndc_hdf5
@@ -26,6 +30,9 @@ env:
     - OPENMC_MULTIPOLE_LIBRARY=$HOME/multipole_lib
     - PATH=$PATH:$HOME/NJOY2016/build
     - DISPLAY=:99.0
+    - CC=gcc-4.9
+    - CXX=g++-4.9
+    - FC=gfortran-4.9
   matrix:
     - OMP=n MPI=n PHDF5=n
     - OMP=y MPI=n PHDF5=n

CMakeLists.txt

@@ -84,8 +84,8 @@ if(CMAKE_Fortran_COMPILER_ID STREQUAL GNU)
   # Make sure version is sufficient
   execute_process(COMMAND ${CMAKE_Fortran_COMPILER} -dumpversion
     OUTPUT_VARIABLE GCC_VERSION)
-  if(GCC_VERSION VERSION_LESS 4.8)
-    message(FATAL_ERROR "gfortran version must be 4.8 or higher")
+  if(GCC_VERSION VERSION_LESS 4.9)
+    message(FATAL_ERROR "gcc version must be 4.9 or higher")
   endif()
 
   # GCC compiler options

docs/source/devguide/styleguide.rst

@@ -174,9 +174,7 @@ Follow the `C++ Core Guidelines`_ except when they conflict with another
 guideline listed here. For convenience, many important guidelines from that
 list are repeated here.
 
-Conform to the C++11 standard. Note that this is a significant difference
-between our style and the C++ Core Guidelines.  Many suggestions in those
-Guidelines require C++14.
+Conform to the C++14 standard.
 
 Always use C++-style comments (``//``) as opposed to C-style (``/**/``). (It
 is more difficult to comment out a large section of code that uses C-style