update .gitignore with Doxyfile.core
diff --git a/.gitignore b/.gitignore
index d072f64..b4d657f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,7 +23,7 @@
 libtool
 libosmocore-*.tar.*
 
-Doxyfile
+Doxyfile.core
 Doxyfile.gsm
 Doxyfile.vty
 Doxyfile.codec