fix lifetime name (#1431)

Author: tshepang

Diff for: src/type-inference.md

@@ -45,11 +45,9 @@ tcx.infer_ctxt().enter(|infcx| {
 })
 ```
 
-Within the closure, `infcx` has the type `InferCtxt<'cx, 'tcx>` for some
-fresh `'cx`, while `'tcx` is the same as outside the inference context.
-(Again, see the [`ty` chapter][ty-ch] for more details on this setup.)
-
-[ty-ch]: ty.html
+Within the closure,
+`infcx` has the type `InferCtxt<'a, 'tcx>` for some fresh `'a`,
+while `'tcx` is the same as outside the inference context.
 
 The `tcx.infer_ctxt` method actually returns a builder, which means
 there are some kinds of configuration you can do before the `infcx` is