Fix toString float encoding (#172)

Ensure a round float does contain a decimal point. Otherwise
feeding the output back to the parser would convert to an integer.

Fixes #171

tomltree_write.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"math"
 	"reflect"
 	"sort"
 	"strconv"
@@ -50,6 +51,11 @@ func tomlValueStringRepresentation(v interface{}) (string, error) {
 	case int64:
 		return strconv.FormatInt(value, 10), nil
 	case float64:
+		// Ensure a round float does contain a decimal point. Otherwise feeding
+		// the output back to the parser would convert to an integer.
+		if math.Trunc(value) == value {
+			return strconv.FormatFloat(value, 'f', 1, 32), nil
+		}
 		return strconv.FormatFloat(value, 'f', -1, 32), nil
 	case string:
 		return "\"" + encodeTomlString(value) + "\"", nil