patch 8.1.1162: incorrect coverage information; typo in color name

Problem:    Incorrect coverage information; typo in color name.
Solution:   Fix the typo.  Set environment variables to have a nested Vim
            write the coverage info in another directory.
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 7268480..b685cd6 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -1495,7 +1495,7 @@
 	\ 'hi Tblack ctermfg=Black ctermbg=Lightgrey',
 	\ 'hi Tdarkred ctermfg=Darkred ctermbg=Red',
 	\ 'hi Tdarkgreen ctermfg=Darkgreen ctermbg=Green',
-	\ 'hi Tbrown ctermfg=Brown ctermbg=Yello',
+	\ 'hi Tbrown ctermfg=Brown ctermbg=Yellow',
 	\ 'hi Tdarkblue ctermfg=Darkblue ctermbg=Blue',
 	\ 'hi Tdarkmagenta ctermfg=Darkmagenta ctermbg=Magenta',
 	\ 'hi Tdarkcyan ctermfg=Darkcyan ctermbg=Cyan',