fix stray space

Author: James Li

src/trait/drop.md

@@ -6,7 +6,7 @@ resources that the implementor instance owns.
 
 `Box`, `Vec`, `String`, `File`, and `Process` are some examples of types that
 implement the `Drop` trait to free resources. The `Drop` trait can also be
-manually implemented for any custom data type. 
+manually implemented for any custom data type.
 
 The following example adds a print to console to the `drop` function to announce
 when it is called.