[Mod] travis.yml: remove -j option under gcc-7
[Mod] travis.yml: remove -j option under gcc-7

msincenselee/vnpy,msincenselee/vnpy,msincenselee/vnpy,bigdig/vnpy,vnpy/vnpy,vnpy/vnpy,bigdig/vnpy,bigdig/vnpy,bigdig/vnpy,msincenselee/vnpy