Remove forcing \n via rustfmt

The original idea here was to make sure, on CI, that line endings are
\n. Travis however uses autocrlf, so the check doesn't actually work,
and forcing \n otherwise makes lives of windows folks difficult

closes #2157

rustfmt.toml

@@ -1,3 +1,2 @@
 reorder_modules = false
 use_small_heuristics = "Max"
-newline_style = "Unix"