gun-ipfs: application/json content-type guessing implemented; plus a relevant test

__tests__/plugins/gun-ipfs.test.js

@@ -107,6 +107,12 @@ describe("plugin: gun-ipfs", () => {
     expect(self.log).toHaveBeenCalledWith('gun-ipfs', "   +-- guessed contentType : text/javascript")
     self.log.mockClear()
     
+    try {
+      await self.LibResilientPlugins[0].fetch(self.location.origin + '/test.json')
+    } catch(e) {}
+    expect(self.log).toHaveBeenCalledWith('gun-ipfs', "   +-- guessed contentType : application/json")
+    self.log.mockClear()
+    
     try {
       await self.LibResilientPlugins[0].fetch(self.location.origin + '/test.svg')
     } catch(e) {}

plugins/gun-ipfs.js

@@ -201,6 +201,9 @@ if (typeof window === 'undefined') {
             case 'js':
                 contentType = 'text/javascript';
                 break;
+            case 'json':
+                contentType = 'application/json';
+                break;
             case 'svg':
                 contentType = 'image/svg+xml';
                 break;