Change 'may not compile to 'might not compile'

This is a subtle thing that I brought up on GitHub. Landon made the
change in many files but missed some in 1986 through 1989. I am aware of
a mass typo in the Makefiles but since some Makefiles are pending
changes I'm not doing that yet.

1986/stein/Makefile

@@ -189,7 +189,7 @@ ${PROG}: ${PROG}.c
 
 
 ${PROG}.orig: ${PROG}.orig.c
-	@echo "NOTE: The original source may not compile using modern compilers."
+	@echo "NOTE: The original source might not compile using modern compilers."
 	-${RM} -f a.out
 	${CC} ${CFLAGS} $< -o $@ ${LIBS}
 	-${LN} $@ a.out