Removing build and dist for Plan 9 due to some issues.

Note, Plan 9 does not implement the syscall interface the same way
other operating systems do. This causes issues in error handling.

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 034c9e2..b254449 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@
 - #580: cross-device error handling failed on Windows in some cases
 - #590: When exit signal received remove global lock
 
+Note, Plan 9 is an experimental OS for Go. Due to some issues we are not going
+to be supporting builds for it at this time.
+
 # Release 0.12.0 (2016-08-23)
 
 ## Added

Makefile

diff --git a/Makefile b/Makefile
index 05fcaeb..a71b9db 100644
--- a/Makefile
+++ b/Makefile
@@ -31,7 +31,7 @@
 build-all:
 	gox -verbose \
 	-ldflags "-X main.version=${VERSION}" \
-	-os="linux darwin windows freebsd openbsd netbsd plan9" \
+	-os="linux darwin windows freebsd openbsd netbsd" \
 	-arch="amd64 386 armv5 armv6 armv7 arm64" \
 	-osarch="!darwin/arm64" \
 	-output="dist/{{.OS}}-{{.Arch}}/{{.Dir}}" .