Update bandit20.md

Fix small typo

wargames/bandit/bandit20.md

@@ -8,7 +8,7 @@ Level Goal
 To gain access to the next level, you should use the setuid binary
 in the homedirectory. Execute it without arguments to find out how
 to use it. The password for this level can be found in the usual
-place (/etc/bandit\_pass), after you have used to setuid binary.
+place (/etc/bandit\_pass), after you have used the setuid binary.
 
 Helpful Reading Material
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