Update E0121.md

Dylan-DPC · web-flow · commit dce0f06f953d · 2019-12-20T17:02:39.000+05:30
diff --git a/src/librustc_error_codes/error_codes/E0121.md b/src/librustc_error_codes/error_codes/E0121.md
@@ -1,4 +1,4 @@
-The type placeholder `_` was used withing a type on an item's signature.
+The type placeholder `_` was used within a type on an item's signature.
 
 Erroneous code example:
 

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		-The type placeholder `_` was used withing a type on an item's signature.
	`1`	+The type placeholder `_` was used within a type on an item's signature.
`2`	`2`
`3`	`3`	`Erroneous code example:`
`4`	`4`