standardize name of license file

Author: adavidw

pom.xml

@@ -16,7 +16,7 @@
     <licenses>
         <license>
             <name>SDK License Agreement</name>
-            <url>https://github.com/AuthorizeNet/sdk-java/blob/master/license.txt</url>
+            <url>https://github.com/AuthorizeNet/sdk-java/blob/master/LICENSE.txt</url>
             <distribution>repo</distribution>
         </license>
     </licenses>