Update globals in .eslintrc files

1. Add Map as a global
2. Use readonly/writable over false/true

Change 2 was done to use non-deprecated values (last paragraph of the section):
https://eslint.org/docs/user-guide/configuring/language-options#using-configuration-files-1

.eslintrc.hound.json

@@ -278,8 +278,9 @@
         ]
     },
     "globals": {
-        "OpenSeadragon": true,
-        "define": false,
-        "module": false
+        "OpenSeadragon": "writable",
+        "define": "readonly",
+        "module": "readonly",
+        "Map": "readonly"
     }
 }

.eslintrc.json

@@ -17,9 +17,10 @@
         }
     },
     "globals": {
-        "OpenSeadragon": true,
-        "define": false,
-        "module": false
+        "OpenSeadragon": "writable",
+        "define": "readonly",
+        "module": "readonly",
+        "Map": "readonly"
     },
     "rules": {
         "no-unused-vars": [