reader: Use the modified PATH variable when creating tmp/id.

This fixes the problem described in #31
by passing the modified PATH variable explicitly
when running the cuid tool.

Change-Id: I368aeb19b33a55abe39e1019028bb262820c439e
diff --git a/web/Makefile b/web/Makefile
index d1c5219..1d3314c 100644
--- a/web/Makefile
+++ b/web/Makefile
@@ -14,7 +14,7 @@
 port ?= 8080
 syncbase_port ?= 4000
 cloudsync_port ?= 8000
-id ?= $(shell if test -e tmp/id; then cat tmp/id; else bin/cuid; fi)
+id ?= $(shell if test -e tmp/id; then cat tmp/id; else PATH=$(PATH) bin/cuid; fi)
 
 all: public/bundle.js node_modules
 	@true  # silences watch