Fix backticks in README.

Author: rolandlo

README.md

@@ -331,14 +331,14 @@ This creates a new metadata item of the specified type, name and value.
 This changes the value of an existing field, but will not change its type.
 
 You can't use `set()` to change core fields such as like `width` or
-`interpretation`.  Use `copy()` instead.`
+`interpretation`.  Use `copy()` instead.
 
 Image references will be shared by the operation cache, so modifying an image
 can change an image somewhere else in your program. Before changing an image,
 you must make sure you own a private copy of an image with `copy`.
 
 ```lua
-local new_image = image:copy()`
+local new_image = image:copy()
 new_image:set("orientation", 7)
 ```