⬆️💚 Bump python 3.6.7 conda version

Somehow the old python 3.6.7 has a dependency conflict with gmt 6.0.0rc1 (even though it worked before), causing the docker build to fail! Bumping to a newer version with md5 hash 787937284685efaaa233453b49a9e719 resolves the issue.

Author: weiji14

environment.yml

@@ -7,7 +7,7 @@ dependencies:
   - defaults::cudatoolkit=10.0[md5=4388ad6015992501b042eea5197eb447]
   - conda-forge/label/dev::gmt=6.0.0rc1[md5=983ab0490b3ea8789136267cd7e7ed02]
   - pip=18.1[md5=d68c7e5109ba0bf4b1cfe60f0f47870a]
-  - conda-forge::python=3.6.7[md5=ff0b816922d1f2ccb4c07045cd3863ce]
+  - conda-forge::python=3.6.7[md5=787937284685efaaa233453b49a9e719]
   - conda-forge::libspatialindex=1.9.0[md5=ef8f25a228de3a0dc716566b8d3de593]
   - pip:
     - pipenv==2018.11.26