Capitialization nits

src/black/__init__.py

@@ -1317,7 +1317,7 @@ def assert_equivalent(src: str, dst: str, *, pass_num: int = 1) -> None:
         raise AssertionError(
             f"cannot use --safe with this file; failed to parse source file AST: "
             f"{exc}\n"
-            f"This could be caused by running black with an older python version "
+            f"This could be caused by running Black with an older Python version "
             f"that does not support new syntax used in your source file."
         ) from exc