Add deg and fr as exceptions for 0 value unit omission

lib/visitor/compiler.js

@@ -413,8 +413,8 @@ Compiler.prototype.visitUnit = function(unit){
 
   // Compress
   if (this.compress) {
-    // Always return '0' unless the unit is a percentage or time
-    if ('%' != type && 's' != type && 'ms' != type && 0 == n) return '0';
+    // Always return '0' unless the unit is a percentage, time, degree or fraction
+    if (!(['%', 's', 'ms', 'deg', 'fr'].includes(type)) && 0 == n) return '0';
     // Omit leading '0' on floats
     if (float && n < 1 && n > -1) {
       return n.toString().replace('0.', '.') + type;

test/cases/compress.units.styl

@@ -19,3 +19,13 @@ body
 body
   foo 0s
   foo 0ms
+
+body
+  foo 0deg
+  foo 15deg
+  foo -15deg
+
+body
+  foo 0fr
+  foo 15fr
+  foo -15fr