Fix retain loop for enrichment plugin closure. (#262)

Author: bsneed

Sources/Segment/Plugins.swift

@@ -68,7 +68,7 @@ internal protocol PlatformPlugin: Plugin { }
 public typealias EnrichmentClosure = (_ event: RawEvent?) -> RawEvent?
 public class ClosureEnrichment: Plugin {
     public var type: PluginType = .enrichment
-    public var analytics: Analytics? = nil
+    public weak var analytics: Analytics? = nil
 
     internal let closure: EnrichmentClosure
 

Tests/Segment-Tests/MemoryLeak_Tests.swift

@@ -45,6 +45,11 @@ final class MemoryLeak_Tests: XCTestCase {
         let macLifecycle = analytics.find(pluginType: macOSLifecycleEvents.self)!
         let macMonitor = analytics.find(pluginType: macOSLifecycleMonitor.self)!
         #endif
+        
+        // test that enrichment closure isn't leaked.  was previously a retain loop.
+        analytics.add { event in
+            return event
+        }
 
         analytics.remove(plugin: startupQueue)
         analytics.remove(plugin: segmentDest)