Update mypy to 0.760

An improvement to type inference for collection types was added, which
allowed me to eliminate one annotation.

tildes/requirements-dev.txt

@@ -21,7 +21,6 @@ gunicorn==20.0.4
 html5lib==1.0.1
 hupper==1.9.1             # via pyramid
 idna==2.8                 # via requests
-importlib-metadata==1.3.0  # via pluggy, pytest
 ipython-genutils==0.2.0   # via traitlets
 ipython==7.10.2
 isort==4.3.21             # via pylint
@@ -32,9 +31,9 @@ mako==1.1.0               # via alembic, pyramid-mako
 markupsafe==1.1.1         # via jinja2, mako, pyramid-jinja2
 marshmallow==3.3.0
 mccabe==0.6.1             # via prospector, pylint
-more-itertools==8.0.2     # via pytest, zipp
+more-itertools==8.0.2     # via pytest
 mypy-extensions==0.4.3    # via mypy
-mypy==0.750
+mypy==0.760
 packaging==19.2           # via pytest
 parso==0.5.2              # via jedi
 pastedeploy==2.0.1        # via plaster-pastedeploy
@@ -82,7 +81,7 @@ python-editor==1.0.4      # via alembic
 pyyaml==5.2
 qrcode==6.1
 redis==3.3.11
-regex==2019.12.9          # via black
+regex==2019.12.19         # via black
 repoze.lru==0.7           # via pyramid-debugtoolbar
 requests==2.22.0
 requirements-detector==0.6  # via prospector
@@ -102,7 +101,7 @@ toml==0.10.0              # via black
 traitlets==4.3.3          # via ipython
 transaction==3.0.0        # via pyramid-tm, zope.sqlalchemy
 translationstring==1.3    # via pyramid
-typed-ast==1.4.0          # via astroid, black, mypy
+typed-ast==1.4.0          # via black, mypy
 typing-extensions==3.7.4.1  # via mypy
 urllib3==1.25.7           # via requests, sentry-sdk
 venusian==3.0.0           # via cornice, pyramid
@@ -114,7 +113,6 @@ webencodings==0.5.1       # via bleach, html5lib
 webob==1.8.5              # via pyramid, webtest
 webtest==2.0.33
 wrapt==1.11.2
-zipp==0.6.0               # via importlib-metadata
 zope.deprecation==4.4.0   # via pyramid, pyramid-jinja2
 zope.interface==4.7.1     # via pyramid, pyramid-webassets, transaction, zope.sqlalchemy
 zope.sqlalchemy==1.2

tildes/tildes/models/user/user.py

@@ -291,7 +291,7 @@ class User(DatabaseModel):
     @property
     def auth_principals(self) -> List[str]:
         """Return the user's authorization principals (used for permissions)."""
-        principals: List[str] = []
+        principals = []
 
         # start with any principals manually defined in the permissions column
         if not self.permissions: