Fix categorization for Racket shell scripts.
Fix categorization for Racket shell scripts.

The current implementation categorizes shell scripts written in Racket
as Scheme, which is incorrect.

For example:

```racket
\#!/usr/bin/env racket

\#lang racket

"Hello World!"
```

This should be categorized as Racket, not Scheme. [This file][1]
demonstrates the problem in an existing repository.

[1]: https://github.com/drautb/sketchbook/blob/master/racket/sublime-project-generator/generate-sublime-project.rkt

pcantrell/linguist,CegepVictoriaville/linguist,whitj00/linguist,github/linguist,iblech/linguist,manveru/linguist,Mx7f/linguist,ilyes14/linguist,R4PaSs/linguist,manveru/linguist,scttnlsn/linguist,thejameskyle/linguist,martynbm/linguist,anhongyue/test222,tschf/linguist,davidzchen/linguist,stanhu/linguist,seanders/linguist,phpsgi/linguist,pchaigno/linguist,CoderXpert/linguist,kr/linguist,georgesuperman/linguist,MahmoudFayed/linguist,BerkeleyTrue/linguist,stanhu/linguist,mattn/linguist,martynbm/linguist,assimovt/ling-ist,erkyrath/linguist,MahmoudFayed/linguist,douglas-larocca/linguist,cybernet14/linguist,ammaraskar/linguist,georgesuperman/linguist,JJ/linguist,sebgod/linguist,pchaigno/linguist,mwpastore/linguist,tschf/linguist,ppaulweber/github-linguist,alitalia/linguist,github/linguist,cybernet14/linguist,ppaulweber/github-linguist,steventhanna/linguist,adamkaplan/linguist,SRI-CSL/linguist,matt40k/linguist,pchaigno/linguist,yyx990803/linguist,iblech/linguist,yscho/linguist,a0viedo/linguist,pchaigno/linguist,douglas-larocca/linguist,JJ/linguist,MostAwesomeDude/linguist,a0viedo/linguist,c-lipka/linguist,whitj00/linguist,PsichiX/linguist,sebgod/linguist,jjatria/linguist,jjatria/linguist,stanhu/linguist,osorgin/linguist,thejameskyle/linguist,pcantrell/linguist,nburkley/linguist,JJ/linguist,meunierfrederic/octocatlinguist,alitalia/linguist,erkyrath/linguist,hcatlin/linguist,jtbandes/linguist,ammaraskar/linguist,cokeboL/linguist,erkyrath/linguist,PsichiX/linguist,mcandre/linguist,SRI-CSL/linguist,github/linguist,hcatlin/linguist,chiranjeevjain/linguist,kyoungrok0517/linguist,adamkaplan/linguist,anhongyue/test222,erkyrath/linguist,stanhu/linguist,nburkley/linguist,phpsgi/linguist,yyx990803/linguist,seanders/linguist,kyoungrok0517/linguist,hcutler/linguist,mcandre/linguist,yyx990803/linguist,CoderXpert/linguist,ilyes14/linguist,sebgod/linguist,MadcapJake/linguist,assimovt/ling-ist,CegepVictoriaville/linguist,R4PaSs/linguist,cokeboL/linguist,sagar290/linguist,hcutler/linguist,osorgin/linguist,github/linguist,meunierfrederic/octocatlinguist,yscho/linguist,sebgod/linguist,JJ/linguist,FStarLang/linguist,yyx990803/linguist,jtbandes/linguist,scttnlsn/linguist,MostAwesomeDude/linguist,bluebear94/linguist,jrnold/linguist,jrnold/linguist,matt40k/linguist,BerkeleyTrue/linguist,christop/linguist,kr/linguist,Mx7f/linguist,MadcapJake/linguist,mattn/linguist,mwpastore/linguist,davidzchen/linguist,chiranjeevjain/linguist,ya7lelkom/linguist,c-lipka/linguist,sagar290/linguist,bluebear94/linguist,steventhanna/linguist,ya7lelkom/linguist,christop/linguist,FStarLang/linguist,meunierfrederic/octocatlinguist