"unexport" isn't recognized as a Makefile keyword

[egor-tensin]

Title, basically. unexport (in contrast to export) isn't recognized as a Makefile keyword, although it is. I assume something here needs to be modified:

pygments/pygments/lexers/make.py

Line 87 in 1ea5fc3

(r'(export)(\s+)(?=[\w${}\t -]+\n)',

.