Update bpkg's version info in the release target

Having to change a version number in several places is a pain. This make
target is meant to allow us to change that version in one place (the
VERSION file), and propagate it elsewhere.

Makefile

@@ -5,7 +5,8 @@ all: shpec
 
 release:
 	sed -i '' "s/^\( *\)VERSION=.*/\1VERSION=`cat VERSION`/" bin/shpec install.sh
-	git add install.sh bin/shpec VERSION
+	sed -i '' "s/^\( *\)\"version\":.*/\1\"version\": \"`cat VERSION`\",/" package.json
+	git add install.sh bin/shpec package.json VERSION
 	git commit -m "Release `cat VERSION`" || true
 	git push origin master
 	git tag `cat VERSION`