Update .editorconfig.

Set charset to UTF-8 for everything:
<https://www.gentoo.org/glep/glep-0031.html>.

Trim trailing whitespace in ebuilds:
<https://devmanual.gentoo.org/ebuild-writing/file-format/index.html>.

Signed-off-by: Ronny (tastytea) Gutbrod <gentoo@tastytea.de>

.editorconfig

@@ -4,9 +4,11 @@ root = true
 end_of_line = lf
 insert_final_newline = true
 tab_width = 4
+charset = utf-8
 
 [*.ebuild]
 indent_style = tab
+trim_trailing_whitespace = true
 
 [metadata.xml]
 indent_style = tab