bugfix: Try and fix issue with Base64 reflection

Based on https://github.com/dirs-dev/directories-jvm/blob/aa87fc1705fec69bc7f486dae6910306a50c221a/src/main/resources/META-INF/native-image/dev.dirs/reflect-config.json

Should help out with scalacenter#1718

Author: tgodzik

bloopgun/src/main/graal/reflection.json

@@ -7,5 +7,23 @@
         "allPublicMethods": true,
         "allDeclaredClasses": true,
         "allPublicClasses": true
+    },
+    {
+        "name": "java.util.Base64",
+        "allDeclaredConstructors": true,
+        "allPublicConstructors": true,
+        "allDeclaredMethods": true,
+        "allPublicMethods": true,
+        "allDeclaredClasses": true,
+        "allPublicClasses": true
+    },
+    {
+        "name": "java.util.Base64$Encoder",
+        "allDeclaredConstructors": true,
+        "allPublicConstructors": true,
+        "allDeclaredMethods": true,
+        "allPublicMethods": true,
+        "allDeclaredClasses": true,
+        "allPublicClasses": true
     }
 ]