Converted all nuspec files to UTF-8

UTF-8 is the mandatory character encoding for nuspec files, otherwise all non-ASCII characters get displayed with “�” in the Gallery, e.g.: http://chocolatey.org/packages/modernmix, http://chocolatey.org/packages/start8

Therefore I converted all nuspec files in this directory to UTF-8 and added the XML declaration: `<?xml version="1.0" encoding="utf-8"?>` like specified in the [Chocolatey wiki](https://github.com/chocolatey/chocolatey/wiki/CreatePackages#character-encoding).

I used my node script [cpkg-utf8-conv](https://github.com/TomOne/cpkg-utf8-conv) to accomplish this task.

Maybe you note that some characters of the diff view on this page look weird, but this is a problem of GitHub. The three files *dashlane.nuspec, modernmix.nuspec and start8.nuspec* were saved in the legacy Windows-1252 encoding (often incorrectly called ANSI). In this pull request I converted them to UTF-8, but the diff view on this GitHub page still parses them as Windows-1252. But I can confirm that in the repository these files are fine. Just click on the “View file @ …” button to be convinced.

I hope that this is understandable. Character encodings can be a very confusing topic. :smile: