Fix serializing :host and ::slotted

Fixes parcel-bundler#409

Author: devongovett

src/lib.rs

@@ -5734,6 +5734,8 @@ mod tests {
     minify_test("a:is(:first-child) { color: yellow }", "a:first-child{color:#ff0}");
     minify_test("a:is(:has(.foo)) { color: yellow }", "a:has(.foo){color:#ff0}");
     minify_test("a:is(:is(.foo)) { color: yellow }", "a.foo{color:#ff0}");
+    minify_test(":host(:hover) {color: red}", ":host(:hover){color:red}");
+    minify_test("::slotted(:hover) {color: red}", "::slotted(:hover){color:red}");
   }
 
   #[test]

src/selector.rs

@@ -1324,6 +1324,20 @@ where
       dest.write_char('#')?;
       dest.write_ident(&id.0)
     }
+    Component::Host(selector) => {
+      dest.write_str(":host")?;
+      if let Some(ref selector) = *selector {
+        dest.write_char('(')?;
+        selector.to_css(dest)?;
+        dest.write_char(')')?;
+      }
+      Ok(())
+    }
+    Component::Slotted(ref selector) => {
+      dest.write_str("::slotted(")?;
+      selector.to_css(dest)?;
+      dest.write_char(')')
+    }
     _ => {
       cssparser::ToCss::to_css(component, dest)?;
       Ok(())