fix navBarSubtitleColor - now it will set the navigation subtitle color properly without any effect on the title (#1847)

example/src/screens/Actions.js

     });
   };
 
+  setSubtitle = () => {
+    this.props.navigator.setSubTitle({
+      subtitle: 'New SubTitle!',
+      navigatorStyle: {
+        navBarSubtitleColor: 'red'
+      }
+    });
+  };
+
   toggleTabs = () => {
     const to = this._toggleTabs === 'shown' ? 'hidden' : 'shown';
 
     return (
       <ScrollView style={styles.container}>
         <Row title={'Set Title'} onPress={this.setTitle} />
+        <Row title={'Set Subtitle'} onPress={this.setSubtitle} />
         <Row title={'Toggle Tabs'} onPress={this.toggleTabs} />
         <Row title={'Set Tab Badge'} onPress={this.setTabBadge} />
         <Row title={'Switch To Tab 0'} onPress={this.switchToTab} />

ios/Helpers/RCCTitleViewHelper.m

 
 #import "RCCTitleViewHelper.h"
 #import <React/RCTConvert.h>
+#import "RCCViewController.h"
 #import "RCTHelpers.h"
 
 @implementation RCCTitleView
         return;
     }
     
+    if ([self.viewController isKindOfClass:[RCCViewController class]]) {
+        NSMutableDictionary *mergedStyle = [NSMutableDictionary dictionaryWithDictionary:((RCCViewController*)self.viewController).navigatorStyle];
+        [mergedStyle addEntriesFromDictionary:style];
+        
+        style = mergedStyle;
+    }
+    
     CGRect navigationBarBounds = self.navigationController.navigationBar.bounds;
     
     self.titleView = [[RCCTitleView alloc] initWithFrame:navigationBarBounds];
     labelframe.size = labelSize;
     subtitleLabel.frame = labelframe;
     [subtitleLabel sizeToFit];
-
+    
     [self.titleView addSubview:subtitleLabel];
     
     return subtitleLabel;