[Flatly theme] white close button on toasts' headers

[Odyseus]

Hello, everybody.

While creating my own variation of the Flatly theme, I found that the close buttons are white on toasts headers white backgrounds.

A simple fix would be:

--- a/dist/flatly/_bootswatch.scss
+++ b/dist/flatly/_bootswatch.scss
@@ -237,6 +237,7 @@ $web-font-path: "https://fonts.googleapis.com/css?family=Lato:400,700,400italic&
 // Progress bars ===============================================================

 // Containers ==================================================================
+.toast .close,
 .modal .close{
   color: $black;

Thank you very much @thomaspark and contributors for your work. :+1:

[thomaspark]

@Odyseus, thanks for the bug report. Fix for Flatly and Lumen incoming.