Bug with handling / in interpolation

[nex3]

From https://github.com/sass/sass/issues/2160:

@nex3 confirmed this is a bug. There is currently a sass spec asserting this broken behaviour which is causing LibSass to fail CI.

h1 {
  delayd: #{5% / 2};
  delayd: #{+5% / 2};
  evaled: #{-5% / 2};
}

Sass 3.4.21

h1 {
  delayd: 5%/2;
  delayd: 5%/2;
  evaled: -2.5%;
}

Expected

h1 {
  delayd: 5%/2;
  delayd: 5%/2;
  evaled: -5%/2;
}