Fix integer overflow issue

diff --git a/TomTom.lua b/TomTom.lua
index c86b7e3..ed6dcc1 100755
--- a/TomTom.lua
+++ b/TomTom.lua
@@ -198,7 +198,7 @@ function TomTom:GetKeyArgs(m, f, x, y, title)
 	local x = x * 10000
 	local y = y * 10000

-    local key = string.format("%d:%d:%d:%d:%s", m, f, x*10e4, y*10e4, tostring(title))
+    local key = string.format("%d:%d:%s:%s:%s", m, f, x*10e4, y*10e4, tostring(title))
 	return key
 end