Adjust script section.

Minimal Racket in 6.0+ is very minimal -- raco make and raco test
commands don't exist. Install rackunit.

.travis.yml

@@ -65,11 +65,8 @@ install:
 before_script:
 
 # Here supply steps such as raco make, raco test, etc.
-#
-# Tip: Use `raco pkg install --deps search-auto <pkg>` to install any
-# required packages without getting stuck on a confirmation prompt.
 script:
-  - raco make main.rkt
+  - raco pkg install --scope installation rackunit # in case minimal racket
   - raco test -x .
 
 # NOTE: If your repo is a Racket package with an info.rkt that