Switch trans' from quote to prime in text to match agda code (#1081)

Co-authored-by: Jefferson Carpenter <jefferson@aoeu2code.com>

Author: negatratoron

src/plfa/part1/Equality.lagda.md

@@ -285,7 +285,7 @@ if it improves readability!)
 
 #### Exercise `trans` and `≡-Reasoning` (practice)
 
-Sadly, we cannot use the definition of `trans'` using ≡-Reasoning as the
+Sadly, we cannot use the definition of `trans′` using ≡-Reasoning as the
 definition for trans. Can you see why? (Hint: look at the definition
 of `_≡⟨_⟩_`)