Update installation instruction for CP 1.7+ (#522)

Summary:
This PR updates the installation instruction for Cocoapods 1.7+ as the previous installation instruction was broken for the latest Cocoapods version

Solves https://github.com/facebook/flipper/issues/478 and https://github.com/facebook/flipper/issues/495

## Changelog

- Updated the Documentation
- Updated the sample app
Pull Request resolved: https://github.com/facebook/flipper/pull/522

Test Plan:
- Travis CI
- Also tested locally by building sample app.

Reviewed By: jknoxville

Differential Revision: D16902023

Pulled By: priteshrnandgaonkar

fbshipit-source-id: 19cc01c842f93ab3565c302f8258ca88dbdecfb2

iOS/Tutorial/Podfile

@@ -1,6 +1,6 @@
 project 'Tutorial.xcodeproj'
 swift_version = "4.1"
-flipperkit_version = '0.20.0'
+flipperkit_version = '0.23.4'
 use_frameworks!
 
 target 'Tutorial' do
@@ -17,19 +17,20 @@ target 'Tutorial' do
   # the pre_install section.  This will cause Flipper and
   # it's dependencies to be static and all other pods to
   # be dynamic.
-
   $static_framework = ['FlipperKit', 'Flipper', 'Flipper-Folly',
     'CocoaAsyncSocket', 'ComponentKit', 'DoubleConversion',
     'glog', 'Flipper-PeerTalk', 'Flipper-RSocket', 'Yoga', 'YogaKit',
-    'CocoaLibEvent', 'OpenSSL-Static', 'boost-for-react-native']
+    'CocoaLibEvent', 'openssl-ios-bitcode', 'boost-for-react-native']
 
   pre_install do |installer|
     Pod::Installer::Xcode::TargetValidator.send(:define_method, :verify_no_static_framework_transitive_dependencies) {}
     installer.pod_targets.each do |pod|
-      if $static_framework.include?(pod.name)
-        pod.instance_variable_set(:@host_requires_frameworks, false)
+        if $static_framework.include?(pod.name)
+          def pod.build_type;
+            Pod::Target::BuildType.static_library
+          end
+        end
       end
-    end
   end