BLD: Warning to bump Python buildpack

[csmcallister]

When pushing the application to cloud.gov, the build raises a warning to bump the Python version to 3.6.7

Expected Behavior

Buildpack specifies the correct python version (3.6.7)

Current Behavior

Buildpack specifies 3.6.6

Possible Solution

Update buildpack to specify version as 3.6.x (see this)

Steps to Reproduce (for bugs)

#Log into cloud.gov
cf login -a api.fr.cloud.gov --sso
cf target -o gsa-ogp-pulse -s pulse
#nav to where pulse
cd ~/Documents/GitHub/pulse
make cg_staging
...........
Downloading build artifacts cache...
Downloading app package...
Downloaded app package (12.3M)
Downloaded build artifacts cache (102.5M)
-----> Python Buildpack version 1.6.25
-----> Supplying Python
-----> Installing python 3.6.6
.....
       **WARNING** A newer version of python is available in this buildpack. 
Please adjust your app to use version 3.6.7 instead of version 3.6.6 as soon as possible. 
Old versions of python are only provided to assist in migrating to newer versions.

Context

Being new to this project as well as cloud.gov, I'm not sure how important this warning is.

[csmcallister]

bumped py buildpack to 3.6.8 in 0ad6fb8