minor refactoring

src/main/java/com/sparrowwallet/drongo/crypto/ECIESKeyCrypter.java

@@ -117,7 +117,4 @@ public class ECIESKeyCrypter implements AsymmetricKeyCrypter {
         }
         return out.toByteArray();
     }
-
-    public static class InvalidPasswordException extends RuntimeException {
-    }
 }

src/main/java/com/sparrowwallet/drongo/crypto/InvalidPasswordException.java

@@ -0,0 +1,19 @@
+package com.sparrowwallet.drongo.crypto;
+
+public class InvalidPasswordException extends RuntimeException {
+    public InvalidPasswordException() {
+        super();
+    }
+
+    public InvalidPasswordException(String message) {
+        super(message);
+    }
+
+    public InvalidPasswordException(Throwable cause) {
+        super(cause);
+    }
+
+    public InvalidPasswordException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}