Fix 2-year-old typo (successfull vs successful)

buildpack-deps/content.md

@@ -10,7 +10,7 @@ This stack is designed to be the foundation of a language-stack image.
 
 ## What's included?
 
-The main tags of this image are the full batteries-included approach. With them, a majority of arbitrary `gem install` / `npm install` / `pip install` should be successfull without additional header/development packages.
+The main tags of this image are the full batteries-included approach. With them, a majority of arbitrary `gem install` / `npm install` / `pip install` should be successful without additional header/development packages.
 
 For some language stacks, that doesn't make sense, particularly if linking to arbitrary external C libraries is much less common (as in Go and Java, for example), which is where these other smaller variants can come in handy.