Fix YAML parsing error in .travis.yml
Fix YAML parsing error in .travis.yml

I have no idea what was causing it, but this seems to fix it.

mafiya69/sympy,jerli/sympy,Curious72/sympy,mafiya69/sympy,rahuldan/sympy,jaimahajan1997/sympy,postvakje/sympy,jaimahajan1997/sympy,hargup/sympy,Titan-C/sympy,madan96/sympy,lindsayad/sympy,Titan-C/sympy,souravsingh/sympy,skidzo/sympy,madan96/sympy,skidzo/sympy,chaffra/sympy,sampadsaha5/sympy,yashsharan/sympy,souravsingh/sympy,skidzo/sympy,ChristinaZografou/sympy,lindsayad/sympy,Curious72/sympy,drufat/sympy,jerli/sympy,postvakje/sympy,kaushik94/sympy,drufat/sympy,souravsingh/sympy,Titan-C/sympy,jaimahajan1997/sympy,lindsayad/sympy,kaushik94/sympy,postvakje/sympy,aktech/sympy,drufat/sympy,aktech/sympy,yashsharan/sympy,aktech/sympy,sampadsaha5/sympy,madan96/sympy,kaichogami/sympy,hargup/sympy,hargup/sympy,yashsharan/sympy,ChristinaZografou/sympy,mafiya69/sympy,rahuldan/sympy,chaffra/sympy,jerli/sympy,rahuldan/sympy,Curious72/sympy,kaushik94/sympy,kaichogami/sympy,ChristinaZografou/sympy,kaichogami/sympy,sampadsaha5/sympy,chaffra/sympy