Fixes quandl reader bug
Fixes quandl reader bug

In order for the Quandl.Reader method to be reusable, it must return the correct type of object for derived types.

Phoenix1271/Lean,andrewhart098/Lean,tomhunter-gh/Lean,mabeale/Lean,redmeros/Lean,jameschch/Lean,FrancisGauthier/Lean,kaffeebrauer/Lean,Jay-Jay-D/LeanSTP,redmeros/Lean,Mendelone/forex_trading,squideyes/Lean,QuantConnect/Lean,FrancisGauthier/Lean,jameschch/Lean,kaffeebrauer/Lean,jameschch/Lean,bizcad/Lean,AnObfuscator/Lean,Mendelone/forex_trading,AnshulYADAV007/Lean,StefanoRaggi/Lean,mabeale/Lean,tomhunter-gh/Lean,andrewhart098/Lean,JKarathiya/Lean,redmeros/Lean,AnshulYADAV007/Lean,devalkeralia/Lean,squideyes/Lean,young-zhang/Lean,AnObfuscator/Lean,young-zhang/Lean,StefanoRaggi/Lean,QuantConnect/Lean,kaffeebrauer/Lean,squideyes/Lean,QuantConnect/Lean,StefanoRaggi/Lean,Mendelone/forex_trading,andrewhart098/Lean,bizcad/Lean,bizcad/Lean,Phoenix1271/Lean,JKarathiya/Lean,AlexCatarino/Lean,devalkeralia/Lean,AlexCatarino/Lean,JKarathiya/Lean,JKarathiya/Lean,FrancisGauthier/Lean,Jay-Jay-D/LeanSTP,squideyes/Lean,AlexCatarino/Lean,jameschch/Lean,Phoenix1271/Lean,tomhunter-gh/Lean,bizcad/Lean,redmeros/Lean,young-zhang/Lean,mabeale/Lean,StefanoRaggi/Lean,AnshulYADAV007/Lean,AnshulYADAV007/Lean,Phoenix1271/Lean,kaffeebrauer/Lean,Mendelone/forex_trading,young-zhang/Lean,kaffeebrauer/Lean,FrancisGauthier/Lean,QuantConnect/Lean,AnObfuscator/Lean,AlexCatarino/Lean,Jay-Jay-D/LeanSTP,jameschch/Lean,andrewhart098/Lean,Jay-Jay-D/LeanSTP,devalkeralia/Lean,devalkeralia/Lean,AnshulYADAV007/Lean,AnObfuscator/Lean,StefanoRaggi/Lean,tomhunter-gh/Lean,Jay-Jay-D/LeanSTP,mabeale/Lean