SPRINGFIELD — A think tank once tied to Republican former Gov. Bruce Rauner sued the Illinois State Board of Elections and secretary of state, charging that graduated tax constitutional amendment language is “misleading” as it appears on the General Election ballot and in a pamphlet sent to voters.The Illinois Policy Institute, which describes itself as a libertarian-leaning think tank and has been a leading organization in opposition of the amendment, is joined by three retirees in the lawsuit which asks …