Revert "Use latest excon."

This reverts commit 6e13de0.

It worked for me locally but it broke the Travis build :(.

lib/vcr/library_hooks/excon.rb

@@ -2,7 +2,7 @@
 require 'vcr/request_handler'
 require 'excon'
 
-VCR::VersionChecker.new('Excon', Excon::VERSION, '0.6.5', '0.7').check_version!
+VCR::VersionChecker.new('Excon', Excon::VERSION, '0.6.5', '0.6').check_version!
 
 module VCR
   class LibraryHooks

spec/vcr/library_hooks/excon_spec.rb

@@ -4,9 +4,9 @@
   it_behaves_like 'a hook into an HTTP library', :excon, 'excon', :status_message_not_exposed
 
   it_performs('version checking', 'Excon',
-    :valid    => %w[ 0.6.5 0.7.8 ],
+    :valid    => %w[ 0.6.5 0.6.99 ],
     :too_low  => %w[ 0.5.99 0.6.4 ],
-    :too_high => %w[ 0.8.0 1.0.0 ]
+    :too_high => %w[ 0.7.0 1.0.0 ]
   ) do
     before(:each) { @orig_version = Excon::VERSION }
     after(:each)  { Excon::VERSION = @orig_version }

vcr.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |s|
 
     'faraday'         => '~> 0.7.2',
     'httpclient'      => '~> 2.1.5.2',
-    'excon'           => '~> 0.7.8',
+    'excon'           => '~> 0.6.5',
 
     'timecop'         => '~> 0.3.5',
     'rack'            => '1.1.0',