docs(): CameraPreview, Base64ToGallery and Developer.MD (#343)

-DEVELOPER.md: Corrects 'npm run tslint' instruction to 'npm run lint'
-CameraPreview: Fixes syntax error in hide
-Base64ToGallery: Adds desc of options obj props

src/plugins/base64togallery.ts

@@ -24,7 +24,7 @@ export class Base64ToGallery {
   /**
    * Converts a base64 string to an image file in the device gallery
    * @param {string} data The actual base64 string that you want to save
-   * @param {any} options (optional) An object with properties: prefix, mediaScanner
+   * @param {any} options (optional) An object with properties: prefix: string, mediaScanner: boolean. Prefix will be prepended to the filename. If true, mediaScanner runs Media Scanner on Android and saves to Camera Roll on iOS; if false, saves to Library folder on iOS.  
    * @returns {Promise} returns a promise that resolves when the image is saved.
    */
   @Cordova()

src/plugins/camera-preview.ts

@@ -99,7 +99,7 @@ export class CameraPreview {
   @Cordova({
     sync: true
   })
-  static hide(): voi { };
+  static hide(): void { };
 
   /**
    * Set the default mode for the Flash.