refact:compat DoricJSLoaderManager api

doric-iOS/Pod/Classes/Loader/DoricJSLoaderManager.h

@@ -25,6 +25,8 @@
 #import "DoricAsyncResult.h"
 
 @interface DoricJSLoaderManager : NSObject
++ (instancetype)instance;
+
 - (void)addJSLoader:(id <DoricLoaderProtocol>)loader;
 
 - (DoricAsyncResult <NSString *> *)request:(NSString *)source;

doric-iOS/Pod/Classes/Loader/DoricJSLoaderManager.m

@@ -24,12 +24,18 @@
 #import "DoricMainBundleJSLoader.h"
 #import "DoricHttpJSLoader.h"
 #import "Doric.h"
+#import "DoricSingleton.h"
 
 @interface DoricJSLoaderManager ()
 @property(nonatomic, copy) NSSet <id <DoricLoaderProtocol>> *loaders;
 @end
 
 @implementation DoricJSLoaderManager
+
++ (instancetype)instance {
+    return DoricSingleton.instance.jsLoaderManager;
+}
+
 - (instancetype)init {
     if (self = [super init]) {
         _loaders = [[NSSet alloc] initWithArray:@[