Move FIRAppEnvironmentUtil.m to third_party directory (#89)

Author: paulb777

Firebase/Core/FIRLogger.m

@@ -15,7 +15,7 @@
 #import "Private/FIRLogger.h"
 
 #import "FIRLoggerLevel.h"
-#import "Private/FIRAppEnvironmentUtil.h"
+#import "third_party/FIRAppEnvironmentUtil.h"
 
 #include <asl.h>
 #include <assert.h>

Firebase/Core/Private/FIRAppEnvironmentUtil.h renamed to Firebase/Core/third_party/FIRAppEnvironmentUtil.h

@@ -14,7 +14,7 @@
 
 #import <Foundation/Foundation.h>
 
-#import "Private/FIRAppEnvironmentUtil.h"
+#import "FIRAppEnvironmentUtil.h"
 
 #import <dlfcn.h>
 #import <mach-o/dyld.h>