Fix typo in README (#2323)

Fix typo in README

README.md

@@ -628,7 +628,7 @@ JPGs will remain JPGs). `Paperclip::Thumbnail` uses ImageMagick to process
 images; [ImageMagick's geometry documentation](http://www.imagemagick.org/script/command-line-processing.php#geometry)
 has more information on the accepted style formats.
 
-ImageMagick supports a number of environment variables for controlling its resource limits. For example, you can enfore memory or execution time limits by setting the following variables in your application's process environment:
+ImageMagick supports a number of environment variables for controlling its resource limits. For example, you can enforce memory or execution time limits by setting the following variables in your application's process environment:
 
 * `MAGICK_MEMORY_LIMIT=128MiB`
 * `MAGICK_MAP_LIMIT=64MiB`