unfixed Notes from CRAN check

[sammo3182]

• checking R code for possible problems ... NOTE by_2sd : : no visible binding for global variable '.'
• checking for unstated dependencies in vignettes ... NOTE 'library' or 'require' calls not declared from: 'broom' 'mfx'

For the second one, I added the three packages into the DESCRIPTION under "Suggestions: " according to Hadley. But the note keeps jumping out.