Fix wrong background color for last symbol

[jgerken]

Bash supports setting the background color to default background color since version 2.53 (http://pueblo.sourceforge.net/doc/manual/ansi_color_codes.html). This fix has a glitch when the macOS X Terminal.app is used (my version is 2.7.2 (388.1) on macOS Sierra 10.12.4): the background color is correct but Terminal uses a brighter color for the foreground than is should.

[krayon]

I believe the suggestion I made in Issue #49 to just reset then set colour again is the easiest. It doesn't have any version requirement then.

[jgerken]

I checked the version requirement again and have to admit that I read the website I cited wrong. The version given in the document is not the BASH version but the version of their software. I tried to figure out when the default background color (value 49) was standardized and found the Standard ECMA-48 Control Functions for Coded Character Sets, 5th edition (June 1991) which already lists 49 default background color (implementation-defined) (page 62 in the PDF). Thus, setting the background color to the standard background color is already part of the standard since 1991. Therefore, I assume that it is supported by every terminal used today and can be used any concern.