ext: C files are all explicitly declared in the gemspec

drop them from extra_rdoc_files which made their inclusion implicit

Author: flavorjones

nokogiri.gemspec

@@ -147,6 +147,7 @@ Gem::Specification.new do |spec|
     "ext/java/nokogiri/internals/dom2dtm/DOM2DTMdefaultNamespaceDeclarationNode.java",
     "ext/nokogiri/depend",
     "ext/nokogiri/extconf.rb",
+    "ext/nokogiri/gumbo.c",
     "ext/nokogiri/html4_document.c",
     "ext/nokogiri/html4_element_description.c",
     "ext/nokogiri/html4_entity_lookup.c",
@@ -156,6 +157,7 @@ Gem::Specification.new do |spec|
     "ext/nokogiri/libxml2_polyfill.c",
     "ext/nokogiri/nokogiri.c",
     "ext/nokogiri/nokogiri.h",
+    "ext/nokogiri/test_global_handlers.c",
     "ext/nokogiri/xml_attr.c",
     "ext/nokogiri/xml_attribute_decl.c",
     "ext/nokogiri/xml_cdata.c",
@@ -181,6 +183,7 @@ Gem::Specification.new do |spec|
     "ext/nokogiri/xml_syntax_error.c",
     "ext/nokogiri/xml_text.c",
     "ext/nokogiri/xml_xpath_context.c",
+    "ext/nokogiri/xml_xpath_expression.c",
     "ext/nokogiri/xslt_stylesheet.c",
     "gumbo-parser/CHANGES.md",
     "gumbo-parser/Makefile",
@@ -327,7 +330,6 @@ Gem::Specification.new do |spec|
   spec.bindir = "bin"
   spec.executables = spec.files.grep(/^bin/) { |f| File.basename(f) }
 
-  spec.extra_rdoc_files += Dir.glob("ext/nokogiri/*.c")
   spec.extra_rdoc_files += Dir.glob("README.md")
   spec.rdoc_options = ["--main", "README.md"]