7.0.0

• Changed: Updated postcss-selector-parser to version 5.0.0-rc.3
• Changed: Dropped reduce-css-calc as a dependency
• Fixed: Support constant() and env() (#42, #48)
• Fixed: Support custom properties with "calc" in its name (#50)
• Fixed: Remove unnecessary whitespace around * and / (cssnano#625)
• Fixed: Arithmetic bugs around subtraction (#49)
• Fixed: Handling of nested calc statements (reduce-css-calc#49)
• Fixed: Bugs regarding complex calculations (reduce-cs-calc#45)
• Fixed: 100% incorrectly being transformed to 1 (reduce-css-calc#44)
• Added: support for case-insensitive calc statements