ABMs: correct typos

Author: rubenwardy

chapters/abms.md

@@ -18,7 +18,7 @@ massive amounts of lag. Use them lightly.
 Special Growing Grass
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-We are now going to make a mod (Yay!).
+We are now going to make a mod (yay!).
 It will add a type of grass called alien grass - it grows near water on grassy
 blocks.