Auto merge of #3889 - alexcrichton:toml-fix, r=alexcrichton
Auto merge of #3889 - alexcrichton:toml-fix, r=alexcrichton

Update toml to fix a regression in backcompat

Related to rust-lang/rust#40956

tsurai/cargo,achanda/cargo,achanda/cargo,rustyhorde/cargo,durka/cargo,rust-lang/cargo,tsurai/cargo,eminence/cargo,vojtechkral/cargo,tshepang/cargo,vojtechkral/cargo,vojtechkral/cargo,nipunn1313/cargo,rust-lang/cargo,tshepang/cargo,nipunn1313/cargo,tshepang/cargo,tshepang/cargo,durka/cargo,vojtechkral/cargo,eminence/cargo,rustyhorde/cargo,rustyhorde/cargo,eminence/cargo,eminence/cargo,tsurai/cargo,durka/cargo,rustyhorde/cargo,achanda/cargo,rust-lang/cargo,achanda/cargo,tsurai/cargo,durka/cargo,nipunn1313/cargo,nipunn1313/cargo,tsurai/cargo,rust-lang/cargo