fix typo

Co-authored-by: Michael Tautschnig <mt@debian.org>

doc/src/challenges/0011-floats-ints.md

@@ -16,7 +16,7 @@ Verify the safety of public unsafe methods for floats and integers in `core::num
 
 ### Part 1: Unsafe Integer Methods
 
-Prove the absence of undefined behavior in the following methods for each of the listed integers types, given that their safety preconditions are satisfied:
+Prove the absence of undefined behavior in the following methods for each of the listed integer types, given that their safety preconditions are satisfied:
 
 | Method | Integer Types |
 | :--- | :---