[varLib] Use Tag() in fvar

Lib/fontTools/ttLib/tables/_f_v_a_r.py

@@ -139,7 +139,7 @@ class Axis(object):
         for tag, _, value in filter(lambda t: type(t) is tuple, content):
             value = ''.join(value)
             if tag == "AxisTag":
-                self.axisTag = value
+                self.axisTag = Tag(value)
             elif tag in ["MinValue", "DefaultValue", "MaxValue", "NameID"]:
                 setattr(self, tag[0].lower() + tag[1:], safeEval(value))
 

Lib/fontTools/varLib/__init__.py

@@ -52,7 +52,7 @@ def _add_fvar(font, axes, axis_names, instances):
 
 	for tag in sorted(axes.keys()):
 		axis = Axis()
-		axis.axisTag = tag
+		axis.axisTag = Tag(tag)
 		axis.minValue, axis.defaultValue, axis.maxValue = axes[tag]
 		axis.nameID = _AddName(font, axis_names[tag]).nameID
 		fvar.axes.append(axis)