chore: Upgrade PyGithub to 1.55

Frappe has upgraded to PyJWT>2. Upgrading PyGithub to resolve
dependency issues
diff --git a/requirements.txt b/requirements.txt
index e30746a..f28906a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,7 +5,7 @@
 pandas~=1.1.5
 plaid-python~=7.2.1
 pycountry~=20.7.3
-PyGithub~=1.54.1
+PyGithub~=1.55
 python-stdnum~=1.16
 python-youtube~=0.8.0
 taxjar~=1.9.2