Fix for contentView nullable; publish v2.1.5

Fixes #102

SMCalloutView.h

@@ -6,7 +6,7 @@
 SMCalloutView
 -------------
 Created by Nick Farina (nfarina@gmail.com)
-Version 2.1.4
+Version 2.1.5
 
 */
 
@@ -81,7 +81,7 @@ extern NSTimeInterval const kSMCalloutViewRepositionDelayForUIScrollView;
 @property (nonatomic, strong, nullable) UIView *subtitleView;
 
 /// Custom "content" view that can be any width/height. If this is set, title/subtitle/titleView/subtitleView are all ignored.
-@property (nonatomic, retain) UIView *contentView;
+@property (nonatomic, retain, nullable) UIView *contentView;
 
 /// Custom content view margin
 @property (nonatomic, assign) UIEdgeInsets contentViewInset;

SMCalloutView.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name         = "SMCalloutView"
-  s.version      = "2.1.4"
+  s.version      = "2.1.5"
   s.summary      = "A lightweight callout view class for iOS mimicking UICalloutView."
   s.description  = <<-DESC
                     SMCalloutView aims to be an exact replica of the private UICalloutView system control.
@@ -10,7 +10,7 @@ Pod::Spec.new do |s|
   s.homepage     = "https://github.com/nfarina/calloutview"
   s.license      = 'Apache License, Version 2.0'
   s.author       = { "Nick Farina" => "nfarina@gmail.com" }
-  s.source       = { :git => "https://github.com/nfarina/calloutview.git", :tag => "2.1.4" }
+  s.source       = { :git => "https://github.com/nfarina/calloutview.git", :tag => "2.1.5" }
   s.platform     = :ios, '7.0'
   s.source_files = 'SMCalloutView.{h,m}', 'SMClassicCalloutView.{h,m}'
   s.requires_arc = true