rename requesterState to RequestContext

Change-Id: I747559b4da11b350b01494c7c54a674c3d3d45f9
diff --git a/src/detail/challenge-encoder.cpp b/src/detail/challenge-encoder.cpp
index fed4110..33559c8 100644
--- a/src/detail/challenge-encoder.cpp
+++ b/src/detail/challenge-encoder.cpp
@@ -40,7 +40,7 @@
 }
 
 void
-ChallengeEncoder::decodeDataContent(const Block& data, requester::RequesterState& state)
+ChallengeEncoder::decodeDataContent(const Block& data, requester::RequestContext& state)
 {
   data.parse();
   state.m_status = static_cast<Status>(readNonNegativeInteger(data.get(tlv::Status)));