Include ternary example in error message

Closes gh-103

Author: philwebb

spring-javaformat/spring-javaformat-checkstyle/src/main/resources/io/spring/javaformat/checkstyle/check/messages.properties

@@ -17,4 +17,4 @@ methodorder.outOfOrder=Method ''{0}'' is out of order, expected {1}.
 methodvisibility.publicMethod=Method ''{0}'' in private class should not be public.
 nothis.unexpected=Reference to instance variable ''{0}'' should not use \"this.\".
 ternary.equalOperator=Ternary operation should use != when testing.
-ternary.missingParen=Ternary operation missing parentheses.
+ternary.missingParen=Ternary operation missing parentheses. Use the form \"(a != b) ? y : n\"

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/check/TernaryParensInvalid.txt

@@ -1,2 +1,2 @@
-+Ternary operation missing parentheses
++Ternary operation missing parentheses. Use the form "(a != b) ? y : n"
 +3 errors