[build] Travis build with make -j$(nproc). (#1454)
[build] Travis build with make -j$(nproc). (#1454)

Ninja provided similar build time, but complicated the build config file.
Haivision/srt,ethouris/srt,Haivision/srt,Cinegy/srt,Cinegy/srt,Haivision/srt,ethouris/srt,Haivision/srt,ethouris/srt,ethouris/srt,Cinegy/srt,Cinegy/srt