change data type in rpc from short to byte for fitting v0.12 (#10)

diff --git a/client/session.go b/client/session.go
index a0901a1..a7ed4ec 100644
--- a/client/session.go
+++ b/client/session.go
@@ -486,7 +486,7 @@
 func valuesToBytes(dataTypes []TSDataType, values []interface{}) ([]byte, error) {
 	buff := &bytes.Buffer{}
 	for i, t := range dataTypes {
-		binary.Write(buff, binary.BigEndian, int16(t))
+		binary.Write(buff, binary.BigEndian, byte(t))
 		v := values[i]
 		if v == nil {
 			return nil, fmt.Errorf("values[%d] can't be nil", i)