Remove call to deprecated method & add type hint to parameter to avoid reflection

[laczoka]

Symptom:

Reflection warning, cheshire/core.clj:63:3 - call to method createJsonGenerator on com.fasterxml.jackson.core.JsonFactory can't be resolved (argument types: unknown).

Check:
https://github.com/FasterXML/jackson-core/blob/master/src/main/java/com/fasterxml/jackson/core/JsonFactory.java#L1132
and #L1145

createJsonGenerator method is deprecated since jackson 2.2, should use createGenerator

to avoid reflection add a type hint

(defn create-generator [writer]
"Returns JsonGenerator for given writer."
(.createGenerator
^JsonFactory (or factory/json-factory
factory/json-factory) ^java.io.Writer writer))

[dakrone]

Fixed, thanks for reporting this!