Remove grep leak

src/bin/sfdoc

@@ -141,7 +141,7 @@ main() {
         man)
             which pod2man &>/dev/null \
              || die "pod2man is missing cannot use man page mode"
-            man --version |& grep -F 'man 2.' \
+            man --version |& grep -qF 'man 2.' \
              || die "unknown \`man\` (only 2.x is supported): $(man --version 2>&1)"
             sfdoc__export manpage "${RealModuleName:-$module}" "$mpath" "$encoding" \
               | man -l -