Merge pull request #24 from SheetJS/master

Makefile use `cut -b` for OSX compatibility

Makefile

@@ -8,7 +8,7 @@ TMP_PATH    := /tmp/${NPM_PACKAGE}-$(shell date +%s)
 REMOTE_NAME ?= origin
 REMOTE_REPO ?= $(shell git config --get remote.${REMOTE_NAME}.url)
 
-CURR_HEAD   := $(firstword $(shell git show-ref --hash HEAD | cut --bytes=-6) master)
+CURR_HEAD   := $(firstword $(shell git show-ref --hash HEAD | cut -b -6) master)
 GITHUB_PROJ := nodeca/${NPM_PACKAGE}