Fix build help

Author: DZakh

jscomp/bsb_exe/rescript_main.ml

@@ -90,7 +90,7 @@ let clean_usage =
 let build_usage =
   "Usage: rescript build <options> -- <ninja_options>\n\n\
    `rescript build` builds the project with dependencies\n\n\
-   `rescript -- -h` for Ninja options (internal usage only; unstable)\n"
+   `rescript build -- -h` for Ninja options (internal usage only; unstable)\n"
 
 let install_target () =
   let ( // ) = Filename.concat in

jscomp/build_tests/cli_help/input.js

@@ -29,7 +29,7 @@ const buildHelp =
   "\n" +
   "`rescript build` builds the project with dependencies\n" +
   "\n" +
-  "`rescript -- -h` for Ninja options (internal usage only; unstable)\n" +
+  "`rescript build -- -h` for Ninja options (internal usage only; unstable)\n" +
   "\n" +
   "Options:\n" +
   "  -w          Watch mode\n" +