Bump libxml-ruby to fix build failure

xml4r/libxml-ruby#213
xml4r/libxml-ruby@c7933a7

Author: CodingItWrong

Gemfile.lock

@@ -305,7 +305,7 @@ GEM
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
     language_server-protocol (3.17.0.3)
-    libxml-ruby (5.0.0)
+    libxml-ruby (5.0.3)
     listen (3.8.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)