Bump nix version to 0.6

inre · inre · commit ceac3575d929 · 2016-07-27T15:01:26.000+03:00
diff --git a/Cargo.toml b/Cargo.toml
@@ -16,4 +16,4 @@ half-duplex SPI access, and full-duplex SPI access.
 [dependencies]
 libc = "^0.2.2"
 bitflags = "^0.3.3"
-nix = "^0.5.0"
+nix = "^0.6.0"
