fixed packages.config not to require v.16 episerver libraries

Hi Mark, 

Thank you for you effort!

I was trying to use your nuget package on EPiServer 7.0 (with assembly versions 7.0.*.1) and got the exception listed below. your .nuspec stated v.1 as refernces, so I think it's ok to downgrade actual references inside your solution. 

Unable to load one or more of the requested types. The following information may be a subset of the Type/LoaderException information present - inspect with debugger for complete view.
Check assemblies [POSSIBLE.RobotsTxtHandler, Version=1.0.3.0, Culture=neutral, PublicKeyToken=null] and/or types [POSSIBLE.RobotsTxtHandler.IRobotsContentService,
POSSIBLE.RobotsTxtHandler.RobotsTxtData,
POSSIBLE.RobotsTxtHandler.RobotsContentService,
POSSIBLE.RobotsTxtHandler.UI.Controllers.RobotsTxtController,
POSSIBLE.RobotsTxtHandler.UI.Models.RobotsTxtViewModel,
POSSIBLE.RobotsTxtHandler.UI.Controllers.RobotsTxtAdminController,
<>f__AnonymousType0`2,
<>f__AnonymousType1`2]. Information from LoaderExceptions property [Could not load file or assembly 'EPiServer.Framework, Version=7.0.859.16, Culture=neutral, PublicKeyToken=8fe83dea738b45b7' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040),
Could not load file or assembly 'EPiServer.Framework, Version=7.0.859.16, Culture=neutral, PublicKeyToken=8fe83dea738b45b7' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)].