Revert "Type MApping: a long gets mapped to integer in Jet" (#151)

This reverts commit 05b10ea856.

src/EFCore.Jet/Storage/Internal/JetTypeMappingSource.cs

@@ -35,7 +35,7 @@ namespace EntityFrameworkCore.Jet.Storage.Internal
         private readonly JetByteTypeMapping _byte = new JetByteTypeMapping("byte", DbType.Byte); // unsigned, there is no signed byte in Jet
         private readonly ShortTypeMapping _smallint = new ShortTypeMapping("smallint", DbType.Int16);
         private readonly IntTypeMapping _integer = new JetIntTypeMapping("integer");
-        private readonly JetLongTypeMapping _bigint = new JetLongTypeMapping("integer");//a long and integer are the same in Jet
+        private readonly JetLongTypeMapping _bigint = new JetLongTypeMapping("decimal");
 
         private readonly JetFloatTypeMapping _single = new JetFloatTypeMapping("single");
         private readonly JetDoubleTypeMapping _double = new JetDoubleTypeMapping("double");