make environment variable strings public again (#132)

prior to #107 (released in version
2.10.0), they were public.

Co-authored-by: David Byron <[email protected]>

Author: dbyron0

src/main/java/com/timgroup/statsd/NonBlockingStatsDClient.java

@@ -54,9 +54,9 @@
  */
 public class NonBlockingStatsDClient implements StatsDClient {
 
-    static final String DD_DOGSTATSD_PORT_ENV_VAR = "DD_DOGSTATSD_PORT";
-    static final String DD_AGENT_HOST_ENV_VAR = "DD_AGENT_HOST";
-    static final String DD_ENTITY_ID_ENV_VAR = "DD_ENTITY_ID";
+    public static final String DD_DOGSTATSD_PORT_ENV_VAR = "DD_DOGSTATSD_PORT";
+    public static final String DD_AGENT_HOST_ENV_VAR = "DD_AGENT_HOST";
+    public static final String DD_ENTITY_ID_ENV_VAR = "DD_ENTITY_ID";
     private static final String ENTITY_ID_TAG_NAME = "dd.internal.entity_id" ;
 
     enum Literal {