Skip string tag tests on Go 1.3 and 1.2
Skip string tag tests on Go 1.3 and 1.2

pquerna/ffjson,cw2018/ffjson,jamesliu96/ffjson,cw2018/ffjson,sunminghong/ffjson,xiuzhifu/ffjson,xladykiller/ffjson,xiuzhifu/ffjson,jamesliu96/ffjson,cmeon/ffjson,trigrass2/ffjson,xyliuke/ffjson,cmeon/ffjson,pquerna/ffjson,xladykiller/ffjson,xyliuke/ffjson,sunminghong/ffjson,trigrass2/ffjson