Fix typo in README.md regarding Hypothesis flag

Author: cclauss

README.md

@@ -75,7 +75,7 @@ those fixtures are shared between threads.
     - `--mark-hypothesis-as-unsafe` to always skip running tests that
       use [hypothesis](https://github.com/hypothesisworks/hypothesis).
       While newer versions of Hypothesis are thread-safe, and versions
-      which are not automatically skipped by `pytest-run-parallel`,
+      which are not are automatically skipped by `pytest-run-parallel`,
       this flag is an escape hatch in case you run into thread-safety
       problems caused by Hypothesis, or in tests that happen to use
       hypothesis and were skipped in older versions of pytest-run-parallel.