create new mappers for each test case (wrong state being kept by jackson-databind)

Author: pjfanning

src/test/scala/com/fasterxml/jackson/module/scala/deser/EitherDeserializerTest.scala

@@ -101,6 +101,10 @@ class EitherDeserializerTest extends DeserializerTest with EitherJsonTestSupport
     deserialize("""{"either":{"r":{"a":"1","b":null,"c":1}}}""", typeRef) shouldBe EitherField(Right(PlainPojoObject("1", None, 1)))
     deserialize("""{"either":{"right":{"a":"1","b":null,"c":1}}}""", typeRef) shouldBe EitherField(Right(PlainPojoObject("1", None, 1)))
   }
+
+  override def deserialize[T](value: String, typeReference: TypeReference[T]): T = {
+    newMapper.readValue(value, typeReference)
+  }
 }