Fix typo: provide -> provider

Author: invzhi

zh/06.2.md

@@ -95,10 +95,10 @@ var provides = make(map[string]Provider)
 // it panics.
 func Register(name string, provider Provider) {
 	if provider == nil {
-		panic("session: Register provide is nil")
+		panic("session: Register provider is nil")
 	}
 	if _, dup := provides[name]; dup {
-		panic("session: Register called twice for provide " + name)
+		panic("session: Register called twice for provider " + name)
 	}
 	provides[name] = provider
 }