Update heroku + travis to python 3.7

.travis.yml

@@ -1,7 +1,8 @@
+dist: xenial
 language: python
 
 python:
-  - "3.6"
+  - "3.7"
 
 addons:
   postgresql: "9.6"
@@ -60,6 +61,8 @@ matrix:
     - name: Percy tests
       if: NOT TRAVIS_PULL_REQUEST_BRANCH =~ /^(dependabot\/)/
       before_install:
+        # libgconf is required by cypress
+        - sudo apt-get install -y libgconf-2-4
         - nvm install --lts=carbon
         - nvm use --lts=carbon
       install:

README.md

@@ -33,7 +33,7 @@ If you installed [Python with Homebrew](https://docs.brew.sh/Homebrew-and-Python
 
 ### Check your environment
 
-- `python --version` should return 3.6 or higher,
+- `python --version` should return 3.7 or higher,
 - `pipenv --version` should return 11.10 or higher,
 - `invoke --version` should return 0.22.1 or higher.
 

runtime.txt

@@ -1 +1 @@
-python-3.6.8
+python-3.7.3