In usr.bin/vacation/Makefile, fix a typo in the comment about clang warnings.
In usr.bin/vacation/Makefile, fix a typo in the comment about clang
warnings.

Spotted by:	arundel
MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase