refactor: rename podspec to openiap with OpenIAP module name

Author: hyochan

README.md

@@ -62,7 +62,7 @@ Or through Xcode:
 Add to your `Podfile`:
 
 ```ruby
-pod 'openiap', '~> 1.0.0'
+pod 'openiap'
 ```
 
 Then run:

openiap.podspec

@@ -1,5 +1,5 @@
 Pod::Spec.new do |s|
-  s.name             = 'OpenIAP'
+  s.name             = 'openiap'
   s.version          = '1.1.0'
   s.summary          = 'OpenIAP - Modern Swift library for in-app purchases'
   s.description      = <<-DESC