[basic.contract.eval] Replace "operation" with "evaluation"

Author: lprv

source/basic.tex

@@ -7786,7 +7786,7 @@
 \pnum
 There is an observable checkpoint\iref{intro.abstract} $C$
 that happens before $A$
-such that any other operation $O$
+such that any other evaluation
 that happens before $A$
 also happens before $C$.
 
@@ -7951,7 +7951,7 @@
 \pnum
 There is an observable checkpoint\iref{intro.abstract} $C$
 that happens after the contract-violation handler returns normally
-such that any other operation $O$
+such that any other evaluation
 that happens after the contract-violation handler returns
 also happens after $C$.