Update policy.md

Fix typo 18-F to 18F

Author: epicfaace

open-source-policy/policy.md

@@ -156,7 +156,7 @@ open source policy, created based on OMB's M-16-21 policy.
 
 ## Thanks ##
 
-CISA would like to thank 18-F, Consumer Financial Protection Bureau, Department
+CISA would like to thank 18F, Consumer Financial Protection Bureau, Department
 of Defense, and Office of Management and Budget for their work in blazing the
 path for the use of FOSS in the Federal Government.