Rename internal CMagicGem implementation

src/main/java/cn/infstar/magicgem/reward/RewardException.java

@@ -0,0 +1,11 @@
+package cn.infstar.magicgem.reward;
+
+public final class RewardException extends Exception {
+    public RewardException(String message) {
+        super(message);
+    }
+
+    public RewardException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}