aws/defaults: Fix UserAgent execution environment key (#307)

Fixes the SDK's UserAgent key for the execution environment.

Fix #276

Author: jasdel

aws/defaults/user_agent_handlers.go

@@ -16,7 +16,7 @@ var SDKVersionUserAgentHandler = aws.NamedHandler{
 }
 
 const execEnvVar = `AWS_EXECUTION_ENV`
-const execEnvUAKey = `exec_env`
+const execEnvUAKey = `exec-env`
 
 // AddHostExecEnvUserAgentHander is a request handler appending the SDK's
 // execution environment to the user agent.

aws/defaults/user_agent_handlers_test.go

@@ -13,9 +13,9 @@ func TestAddHostExecEnvUserAgentHander(t *testing.T) {
 		ExecEnv string
 		Expect  string
 	}{
-		{ExecEnv: "Lambda", Expect: "exec_env/Lambda"},
+		{ExecEnv: "Lambda", Expect: execEnvUAKey + "/Lambda"},
 		{ExecEnv: "", Expect: ""},
-		{ExecEnv: "someThingCool", Expect: "exec_env/someThingCool"},
+		{ExecEnv: "someThingCool", Expect: execEnvUAKey + "/someThingCool"},
 	}
 
 	for i, c := range cases {