v1.2.6

- Disabled mapping to designspace's internal space when using varLib's
  interpolate_layout (#321). Fixes https://github.com/fonttools/fonttools/issues/950

Updated minimum requirements:

- fonttools >= 3.13.0
  * Adds `mapped` keyword argument to varLib.interpolate_layout.
  * Fixed bug with recombining PairPosClass2 subtables.
- cu2qu >= 1.2.0
  * Uses 0.001 as default approximation error for cubic to quadratic
    conversion. To keep using the previous value, you can pass the option
    -e 0.0025.
- ufo2ft >= 0.5.3
  * Only writeFeatures_mark if neither mark or mkmk is present.
- defcon >= 0.3.3
  * minor bugfixes.
- glyphsLib >= 1.7.5:
  * support 'codePageRanges', 'GASP Table' and 'openTypeHeadFlags' custom
    parameters.