fix: change firestore default settings version comparison

Change the condition that determines whether timestampsInSnapshots setting is set to true.
This is done to order to comply with multiple digits minor versions of firebase sdk.
For example: version 5.10.0 is greater than 5.8.0

fixes angular#2050

Author: ron4548

src/firestore/firestore.ts

@@ -19,7 +19,9 @@ export const PersistenceSettingsToken = new InjectionToken<PersistenceSettings|u
 export const FirestoreSettingsToken = new InjectionToken<Settings>('angularfire2.firestore.settings');
 
 // timestampsInSnapshots was depreciated in 5.8.0
-export const DefaultFirestoreSettings = (parseFloat(SDK_VERSION) < 5.8 ? {timestampsInSnapshots: true} : {}) as Settings;
+const major = parseInt(SDK_VERSION.split('.')[0]);
+const minor = parseInt(SDK_VERSION.split('.')[1]);
+export const DefaultFirestoreSettings = ((major < 5 || (major == 5 && minor < 8)) ? {timestampsInSnapshots: true} : {}) as Settings;
 
 /**
  * A utility methods for associating a collection reference with