Fixing typo in PROBLEMS

Signed-off-by: NRich Salz <rsalz@akamai.com>
Reviewed-by: NAndy Polyakov <appro@openssl.org>

PROBLEMS

@@ -47,7 +47,7 @@ While running tests, running a parallell make is a bad idea.  Many test
 scripts use the same name for output and input files, which means different
 will interfere with each other and lead to test failure.
 
-The solution is simple for now: don't run parallell make when testing.
+The solution is simple for now: don't run parallel make when testing.
 
 
 * Bugs in gcc triggered