Stub File.read instead of IO.read in spec.

Ruby 2.6 changed Pathname#read from using IO.read to File.read.

spec/lib/guard/guardfile/generator_spec.rb

@@ -91,7 +91,7 @@
       let(:template) { File.join(described_class::HOME_TEMPLATES, "/bar") }
 
       it "copies the Guardfile template and initializes the Guard" do
-        expect(IO).to receive(:read)
+        expect(File).to receive(:read)
           .with(template).and_return "Template content"
 
         expected = "\nTemplate content\n"
@@ -113,7 +113,7 @@
         expect(::Guard::PluginUtil).to receive(:new) { plugin_util }
         allow(plugin_util).to receive(:plugin_class) { nil }
         path = File.expand_path("~/.guard/templates/foo")
-        expect(IO).to receive(:read).with(path) do
+        expect(File).to receive(:read).with(path) do
           fail Errno::ENOENT
         end
       end

spec/spec_helper.rb

@@ -70,14 +70,14 @@ def stub_file(path, contents = nil, &block)
   allow(File).to receive(:exist?).with(path).and_return(exists)
   if exists
     if block.nil?
-      allow(IO).to receive(:read).with(path).and_return(contents)
+      allow(File).to receive(:read).with(path).and_return(contents)
     else
-      allow(IO).to receive(:read).with(path) do
+      allow(File).to receive(:read).with(path) do
         yield
       end
     end
   else
-    allow(IO).to receive(:read).with(path) do
+    allow(File).to receive(:read).with(path) do
       fail Errno::ENOENT
     end
   end