Fix default Net::HTTP encoding in Windows tests.

It turns out that Net::HTTP seems to always use UTF-8 as the default
encoding, even when Encoding.default_external is Encoding::IBM437 (as it
is on Windows/mingw).

lib/restclient/utils.rb

@@ -8,8 +8,8 @@ module RestClient
     # text. This differs from the older RFC 2616 behavior, which specifies
     # using ISO-8859-1 for text/* content types without a charset.
     #
-    # Strings will effectively end up using `Encoding.default_external` when
-    # this method returns nil.
+    # Strings will use the default encoding when this method returns nil. This
+    # default is likely to be UTF-8 for Ruby >= 2.0
     #
     # @param headers [Hash<Symbol,String>]
     #

spec/integration/integration_spec.rb

@@ -88,14 +88,15 @@ describe RestClient do
       expect(response.encode('utf-8')).to eq body_utf8
     end
 
-    it 'defaults to Encoding.default_external' do
+    it 'defaults to the default encoding' do
       stub_request(:get, 'www.example.com').to_return(
         body: 'abc', status: 200, headers: {
           'Content-Type' => 'text/plain'
         })
 
       response = RestClient.get 'www.example.com'
-      expect(response.encoding).to eq Encoding.default_external
+      # expect(response.encoding).to eq Encoding.default_external
+      expect(response.encoding).to eq Encoding::UTF_8
     end
 
     it 'handles invalid encoding' do
@@ -105,7 +106,8 @@ describe RestClient do
         })
 
       response = RestClient.get 'www.example.com'
-      expect(response.encoding).to eq Encoding.default_external
+      # expect(response.encoding).to eq Encoding.default_external
+      expect(response.encoding).to eq Encoding::UTF_8
     end
 
     it 'leaves images as binary' do