Fix misleading text about duplicate keys in JSON (#141)

Per RFC 8259 Section 4, behavior on duplicate keys is unspecified.

Fixes #140.

README.md

@@ -577,7 +577,7 @@ Log a static string, without any context or `printf`-style templating:
 
 ## Caveats
 
-Note that zerolog does de-duplication fields. Using the same key multiple times creates multiple keys in final JSON:
+Note that zerolog does no de-duplication of fields. Using the same key multiple times creates multiple keys in final JSON:
 
 ```go
 logger := zerolog.New(os.Stderr).With().Timestamp().Logger()
@@ -587,4 +587,4 @@ logger.Info().
 // Output: {"level":"info","time":1494567715,"time":1494567715,"message":"dup"}
 ```
 
-However, it’s not a big deal as JSON accepts dup keys; the last one prevails.
+In this case, many consumers will take the last value, but this is not guaranteed; check yours if in doubt.

log.go

@@ -94,8 +94,8 @@
 //            Msg("dup")
 //     // Output: {"level":"info","time":1494567715,"time":1494567715,"message":"dup"}
 //
-// However, it’s not a big deal though as JSON accepts dup keys,
-// the last one prevails.
+// In this case, many consumers will take the last value,
+// but this is not guaranteed; check yours if in doubt.
 package zerolog
 
 import (