docs: Fix typo in tutorial-1 (#478)

docs/src/tutorials/tutorial-1.md

@@ -122,5 +122,5 @@ anchor test
 ## Next Steps
 
 We've covered all the basics of developing applications using Anchor. However, we've
-left out one import aspect to ensure the security of our programs--validating input
+left out one important aspect to ensure the security of our programs--validating input
 and access control. We'll cover that next.