Edit Parameter Environments's url as it has been edited in rust-lang#1953

Author: surechen

src/appendix/code-index.md

@@ -41,5 +41,5 @@ Item            |  Kind    | Short description           | Chapter            |
 [Emitting Diagnostics]: ../diagnostics.html
 [Macro expansion]: ../macro-expansion.html
 [Name resolution]: ../name-resolution.html
-[Parameter Environment]: ../param_env.html
+[Parameter Environment]: ../param_env/param_env_summary.html
 [Trait Solving: Goals and Clauses]: ../traits/goals-and-clauses.html#domain-goals

src/const-eval.md

@@ -35,7 +35,7 @@ They're the wrappers of the `const_eval` query.
   Statics are special; all other functions do not represent statics correctly
   and have thus assertions preventing their use on statics.
 
-The `const_eval_*` functions use a [`ParamEnv`](./param_env.html) of environment
+The `const_eval_*` functions use a [`ParamEnv`](./param_env/param_env_summary.html) of environment
 in which the constant is evaluated (e.g. the function within which the constant is used)
 and a [`GlobalId`]. The `GlobalId` is made up of an `Instance` referring to a constant
 or static or of an `Instance` of a function and an index into the function's `Promoted` table.

src/traits/caching.md

@@ -61,7 +61,7 @@ to be pretty clearly safe and also still retains a very high hit rate
 **TODO**: it looks like `pick_candidate_cache` no longer exists. In
 general, is this section still accurate at all?
 
-[`ParamEnv`]: ../param_env.html
+[`ParamEnv`]: ../param_env/param_env_summary.html
 [`tcx`]: ../ty.html
 [#18290]: https://github.com/rust-lang/rust/issues/18290
 [#22019]: https://github.com/rust-lang/rust/issues/22019

src/traits/resolution.md

@@ -183,7 +183,7 @@ in that list. If so, it is considered satisfied. More precisely, we
 want to check whether there is a where-clause obligation that is for
 the same trait (or some subtrait) and which can match against the obligation.
 
-[parameter environment]: ../param_env.html
+[parameter environment]: ../param_env/param_env_summary.html
 
 Consider this simple example: