``\\`` is not a path separator for Linux (and maybe Mac)

[tanaka-takayoshi]

Related to case #98
Found this class: https://github.com/VenusInterns/BlogTemplate/blob/master/BlogTemplate/Models/BlogDataStore.cs

\\ would be escaped \ and \ is not a path separator for Linux. For example in the Linux, BlogFiles\Posts direcotry is created. Note that BlogFiles\Posts is not a two directory, but just on directory with name BlogFiles\Posts.

Simply replacing \\ into / or using Path.Join then it works as a path separator for every platform.