added missing package dependency

a 'make in-place' from the main racket repo will error if this package is install:

raco setup: found undeclared dependency:
raco setup:   mode: run
raco setup:   for package: "opengl"
raco setup:   on package: "srfi-lite-lib"
raco setup:   dependent source: /Applications/Racket/racket/share/pkgs/opengl/opengl/compiled/readspec_rkt.zo
raco setup:   used module: (lib "srfi/13.rkt")
raco setup: --- summary of missing dependencies ---
raco setup: undeclared dependency detected
raco setup:   for package: "opengl"
raco setup:   on package:
raco setup:    "srfi-lite-lib"
make[1]: *** [plain-in-place] Error 1
make: *** [in-place] Error 2

This should fix that.