Trivial typo fix

as suggested in #2022

Author: martin-frbg

Makefile.rule

@@ -199,7 +199,7 @@ NO_AFFINITY = 1
 # been reported to be optimal for certain workloads (50 is the recommended value for Julia).
 # GEMM_MULTITHREAD_THRESHOLD = 4
 
-# If you need santy check by comparing reference BLAS. It'll be very
+# If you need sanity check by comparing results to reference BLAS. It'll be very
 # slow (Not implemented yet).
 # SANITY_CHECK = 1