Makefile: always use utf-8 as default locale when compiling sass
Makefile: always use utf-8 as default locale when compiling sass

When building on our ci we use C as our locale, we need to specify
utf-8 as the default there
[endlessm/eos-sdk#2980]

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib