fix match race condition with vars map

[hexadecy]

Since Go 1.6 race condition is better detected.

fatal error: concurrent map read and map write
fatal error: concurrent map read and map write

goroutine 10105 [running]:
runtime.throw(0xa6a2c0, 0x21)
C:/Go/src/runtime/panic.go:530 +0x97 fp=0xc0820639c8 sp=0xc0820639b0
runtime.mapaccess1_fast64(0x86ed40, 0xc082052c90, 0xc082126540, 0x1)
C:/Go/src/runtime/hashmap_fast.go:112 +0x61 fp=0xc0820639e8 sp=0xc0820639c8
local/beenote/vendor/github.com/go-zoo/bone.(_Route).Match(0xc08214c500, 0xc082126540, 0x9e6700)
C:/Workspace/src/local/beenote/vendor/github.com/go-zoo/bone/route.go:98 +0x121 fp=0xc082063b58 sp=0xc0820639e8
local/beenote/vendor/github.com/go-zoo/bone.(_Route).parse(0xc08214c500, 0x2a44338, 0xc082122060, 0xc082126540, 0xc082049100)
C:/Workspace/src/local/beenote/vendor/github.com/go-zoo/bone/route.go:133 +0x196 fp=0xc082063bc0 sp=0xc082063b58

[squiidz]

Merci ;)