Fix type coma->comma

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

src/univers/version_constraint.py

@@ -209,7 +209,7 @@ def to_constraints_string(cls, constraints):
         list of VersionConstraint objects such that the outer sequence
         VersionConstraints are joined with an "OR" e.g., a "vers" pipe "|" and
         the inner sequences of VersionConstraint are each joined with an "AND"
-        e.g., a "vers" coma ",".
+        e.g., a "vers" comma ",".
         For instance:
         >>> from univers.versions import PypiVersion
         >>> constraints = [