travis: Update python from 3.7.2 to 3.7.4

Author: jcfr

.travis.yml

@@ -11,7 +11,7 @@ matrix:
     - os: osx
       language: generic
       env:
-        - PYTHON_VERSION=3.7.2
+        - PYTHON_VERSION=3.7.4
 
     - os: osx
       language: generic
@@ -20,7 +20,7 @@ matrix:
 
 cache:
   directories:
-    - $HOME/.pyenv/versions/3.7.2
+    - $HOME/.pyenv/versions/3.7.4
     - $HOME/.pyenv/versions/2.7.15
     - $HOME/downloads