Fix typo

Author: zohairawan

src/compilation/modules.md

@@ -1,7 +1,7 @@
 # Modules
 
 For reasons that will become apparent as we proceed,
-it is best if all all the code you intend to share
+it is best if all the code you intend to share
 is contained within a named module.
 
 This means at minimum your classes would need to be in packages