fix wrong link

Author: bombless

src/doc/reference.md

@@ -2219,7 +2219,7 @@ For any lint check `C`:
 
 The lint checks supported by the compiler can be found via `rustc -W help`,
 along with their default settings.  [Compiler
-plugins](book/plugin.html#lint-plugins) can provide additional lint checks.
+plugins](book/plugins.html#lint-plugins) can provide additional lint checks.
 
 ```{.ignore}
 mod m1 {
@@ -4369,4 +4369,4 @@ that have since been removed):
   pattern syntax
 
 [ffi]: book/ffi.html
-[plugin]: book/plugin.html
+[plugin]: book/plugins.html