Set SQLDialect.supportsReturning to true (vapor#189)

Author: grahamburgsma

Package.swift

@@ -11,7 +11,7 @@ let package = Package(
     ],
     dependencies: [
         .package(url: "https://github.com/vapor/postgres-nio.git", from: "1.0.0"),
-        .package(url: "https://github.com/vapor/sql-kit.git", from: "3.0.0"),
+        .package(url: "https://github.com/vapor/sql-kit.git", from: "3.5.0"),
         .package(url: "https://github.com/vapor/async-kit.git", from: "1.0.0"),
     ],
     targets: [

Sources/PostgresKit/PostgresDialect.swift

@@ -30,6 +30,10 @@ public struct PostgresDialect: SQLDialect {
         true
     }
 
+    public var supportsReturning: Bool {
+        true
+    }
+
     public var enumSyntax: SQLEnumSyntax {
         .typeName
     }