Homebrew updated to 3.8 yesterday.

Author: henryiii

.travis.yml

@@ -149,7 +149,7 @@ matrix:
   - os: osx
     name: Python 3.7, c++14, AppleClang 9, Debug build
     osx_image: xcode9.4
-    env: PYTHON=3.7 CPP=14 CLANG DEBUG=1
+    env: PYTHON=3.8 CPP=14 CLANG DEBUG=1
   # Test a PyPy 2.7 build
   - os: linux
     dist: trusty