Add space around ~ combinator (#1774)

src/printer.js

@@ -2612,7 +2612,7 @@ function genericPrintNoParens(path, options, print, args) {
       ]);
     }
     case "selector-combinator": {
-      if (n.value === "+" || n.value === ">") {
+      if (n.value === "+" || n.value === ">" || n.value === "~") {
         return concat([" ", n.value, " "]);
       }
       return n.value;

tests/css_combinator/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,10 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`combinator.css 1`] = `
+-Option/root .public/section ~ .public/section:before {
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-Option/root .public/section ~ .public/section:before {
+}
+
+`;

tests/css_combinator/combinator.css

@@ -0,0 +1,2 @@
+-Option/root .public/section ~ .public/section:before {
+}

tests/css_combinator/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, { parser: "postcss" });