[NFC] Inclusive Language: change master to main for .chm files

[NFC] As part of using inclusive language within the llvm project,
this patch replaces master with main when referring to `.chm` files.

Reviewed By: teemperor

Differential Revision: https://reviews.llvm.org/D113299
diff --git a/lldb/docs/doxygen.cfg.in b/lldb/docs/doxygen.cfg.in
index 7750d89..5712779 100644
--- a/lldb/docs/doxygen.cfg.in
+++ b/lldb/docs/doxygen.cfg.in
@@ -916,7 +916,7 @@
 
 # If the GENERATE_HTMLHELP tag is set to YES, the GENERATE_CHI flag
 # controls if a separate .chi index file is generated (YES) or that
-# it should be included in the master .chm file (NO).
+# it should be included in the main .chm file (NO).
 
 GENERATE_CHI           = NO