[chore] tidyconfig: Added explicit indent-spaces.

Fixes HTML Tidy, which changed some time in between 5.7.3 and 5.7.16 to
not indent unless indent-spaces: 2 explicitly appears in the config
file.

Author: mgiuca

tidyconfig.txt

@@ -1,4 +1,5 @@
 char-encoding: utf8
 indent: yes
+indent-spaces: 2
 wrap: 80
 tidy-mark: no