Fix Rubocop warnings

Author: andrykonchin

core/exception/frozen_error_spec.rb

@@ -28,7 +28,7 @@ def o.x; end
 
     -> {
       def object.x; end
-    }.should raise_error(FrozenError, "can't modify frozen object: #{object.to_s}")
+    }.should raise_error(FrozenError, "can't modify frozen object: #{object}")
 
     object = [].freeze
     -> { object << nil }.should raise_error(FrozenError, "can't modify frozen Array: []")

language/def_spec.rb

@@ -97,7 +97,7 @@ def foo(a); end
         def foo; end
       end
     }.should raise_error(FrozenError) { |e|
-      e.message.should == "can't modify frozen module: #{e.receiver.to_s}"
+      e.message.should == "can't modify frozen module: #{e.receiver}"
     }
 
     -> {
@@ -106,7 +106,7 @@ def foo; end
         def foo; end
       end
     }.should raise_error(FrozenError){ |e|
-      e.message.should == "can't modify frozen class: #{e.receiver.to_s}"
+      e.message.should == "can't modify frozen class: #{e.receiver}"
     }
   end
 end
@@ -283,20 +283,20 @@ def obj.==(other)
   it "raises FrozenError with the correct class name" do
     obj = Object.new
     obj.freeze
-    -> { def obj.foo; end }.should raise_error(FrozenError, "can't modify frozen object: #{obj.to_s}")
+    -> { def obj.foo; end }.should raise_error(FrozenError, "can't modify frozen object: #{obj}")
 
     obj = Object.new
     c = obj.singleton_class
     c.singleton_class.freeze
-    -> { def c.foo; end }.should raise_error(FrozenError, "can't modify frozen Class: #{c.to_s}")
+    -> { def c.foo; end }.should raise_error(FrozenError, "can't modify frozen Class: #{c}")
 
     c = Class.new
     c.freeze
-    -> { def c.foo; end }.should raise_error(FrozenError, "can't modify frozen Class: #{c.to_s}")
+    -> { def c.foo; end }.should raise_error(FrozenError, "can't modify frozen Class: #{c}")
 
     m = Module.new
     m.freeze
-    -> { def m.foo; end }.should raise_error(FrozenError, "can't modify frozen Module: #{m.to_s}")
+    -> { def m.foo; end }.should raise_error(FrozenError, "can't modify frozen Module: #{m}")
   end
 end
 

library/stringio/readline_spec.rb

@@ -55,4 +55,4 @@
   describe "when in write-only mode" do
     it_behaves_like :stringio_gets_write_only, :readline
   end
-end
+end

library/stringio/shared/gets.rb

@@ -246,4 +246,4 @@
       -> { io.send(@method) }.should raise_error(IOError)
     end
   end
-end
+end