fix(build): export GOPATH

Major mistake. GOPATH must be exported for go get/go build to work.

build

@@ -1,7 +1,7 @@
 #!/bin/sh
 
 ETCD_PACKAGE=github.com/coreos/etcd
-GOPATH=${PWD}
+export GOPATH=${PWD}
 SRC_DIR=$GOPATH/src
 ETCD_DIR=$SRC_DIR/$ETCD_PACKAGE