Updates the MsBuild script so that an empty ReleaseNoteContentToBeInsertedWihinNuspecFile.txt file won't throw an error (in that case, the script sets a 'n/a' value as release note).

Empties the ReleaseNoteContentToBeInsertedWihinNuspecFile.txt file (to be fill with next version.
Increments the minor version number for NFluent (next version will be 0.7).