Apply suggestion from @skirpichev

Author: skirpichev

pyperformance/data-files/benchmarks/MANIFEST

@@ -37,7 +37,8 @@ chaos	<local>
 comprehensions	<local>
 crypto_pyaes	<local>
 dask	<local>
-decimal_factorial	<local>
+# FIXME: this doesn't work with `_pydecimal`
+# decimal_factorial	<local>
 decimal_pi	<local>
 deepcopy	<local>
 deltablue	<local>