'lib/functions.zsh: Solve typos'

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

lib/functions.zsh

@@ -86,7 +86,7 @@ function default() {
 }
 
 #
-# Set enviroment variable "$1" to default value "$2" if "$1" is not yet defined.
+# Set environment variable "$1" to default value "$2" if "$1" is not yet defined.
 #
 # Arguments:
 #    1. name - The env variable to set