Check if .yml? when updating
Check if .yml? when updating

It's not really about frontmatter vs content.  YAML files simply have no
--- seperators and all other files do.

Closes #73

singpolyma/tint,usetint/tint,singpolyma/tint,ericroberts/tint,ericroberts/tint,usetint/tint,usetint/tint,usetint/tint,ericroberts/tint,singpolyma/tint,ericroberts/tint,singpolyma/tint