Auto merge of #3416 - charlieok:3415_fix_double_slash_error, r=bitcartel

Remove extra slash from lockfile path

Issue: https://github.com/zcash/zcash/issues/3415

After this change I can successfully run `fetch-params` in an msys2 environment.

zcutil/fetch-params.sh

@@ -140,7 +140,7 @@ function lock() {
         fi
     else
         # create lock file
-        eval "exec 200>/$lockfile"
+        eval "exec 200>$lockfile"
         # acquire the lock
         flock -n 200 \
             && return 0 \