Update asserts.py documentation (#1036)

it's been a while Python does not produce anymore .pyo files (see https://docs.python.org/3/using/cmdline.html#cmdoption-O)

bandit/plugins/asserts.py

@@ -9,8 +9,8 @@
 
 This plugin test checks for the use of the Python ``assert`` keyword. It was
 discovered that some projects used assert to enforce interface constraints.
-However, assert is removed with compiling to optimised byte code (python -o
-producing \*.pyo files). This caused various protections to be removed.
+However, assert is removed with compiling to optimised byte code (`python -O`
+producing \*.opt-1.pyc files). This caused various protections to be removed.
 Consider raising a semantically meaningful error or ``AssertionError`` instead.
 
 Please see