Always use https for wsrv.nl usage (#41)

lib/helpers/parse.js

@@ -131,7 +131,7 @@ export const md = (options = {}) => {
       } catch (err) {
         /* empty */
       }
-      token.attrs[index][1] = `//wsrv.nl/?url=${encodeURIComponent(src)}`
+      token.attrs[index][1] = `https://wsrv.nl/?url=${encodeURIComponent(src)}`
     }
 
     return defaultImageRenderer(tokens, idx, options, env, self)