Fix case in .gitignore (GH-2607)

diff --git a/.gitignore b/.gitignore
index 03c8268..ea7abfe 100644
--- a/.gitignore
+++ b/.gitignore
@@ -60,7 +60,7 @@
 PCbuild/.vs/
 PCbuild/amd64/
 PCbuild/obj/
-PCBuild/win32/
+PCbuild/win32/
 .purify
 Parser/pgen
 Parser/pgen.exe