Merge pull request #660 from tskit-dev/dependabot/pip/python/requirements/CI/biopython-1.77

Bump biopython from 1.76 to 1.77 in /python/requirements/CI

Author: mergify[bot]

python/requirements/CI/requirements.txt

@@ -1,5 +1,5 @@
 attrs==19.3.0
-biopython==1.76
+biopython==1.77
 black==19.10b0
 breathe==4.14.2
 codecov==2.1.3