It failed to build when there's a "bytes" field in the "oneof"

```proto
message Frame {
oneof type {
bytes buf = 1;
}
}
```
Reports:
```
Failed to serialize property Buf : System.Byte. error : System.ArgumentException: Type mismatch when building 'f': function argument type doesn't match. Expected 'System.Byte', but received type 'System.ArraySegment`1[System.Byte]'. (Parameter 'receivedType') [/home/xy02/f#/ritp/ritp.fsproj]
at Microsoft.FSharp.Quotations.PatternsModule.checkTypesSR[a](Type expectedType, Type receivedType, a name, String threeHoleSR)
at Microsoft.FSharp.Quotations.PatternsModule.checkAppliedLambda(FSharpExpr f, FSharpExpr v)
at Microsoft.FSharp.Quotations.PatternsModule.mkApplication(FSharpExpr v_0, FSharpExpr v_1)
at Microsoft.FSharp.Quotations.FSharpExpr.Application(FSharpExpr functionExpr, FSharpExpr argument)
at Microsoft.FSharp.Collections.SeqModule.Fold[T,TState](FSharpFunc`2 folder, TState state, IEnumerable`1 source)
at Falanx.Proto.Codec.Binary.Serialization.serializeProperty(FSharpExpr buffer, FSharpExpr this, PropertyDescriptor prop) in D:\a\1\s\src\Falanx.Proto.Core\BinaryCodec\Serialization.fs:line 117
```