Don't collapse line feeds after "return"

return is not guaranteed to be followed by a return value.
It could just be "return", followed by nothing (void return),
not even a semicolon, just line feed (ASI)
Whatever is next could, for example, be another operator.
We may just need ASI to kick in there, so keep the line feed
after return.

Fixes issue #54

data/js/keywords_before.txt

@@ -15,7 +15,6 @@ delete
 export
 import
 public
-return
 static
 typeof
 extends

tests/js/JSTest.php

@@ -575,6 +575,20 @@ function foo(a,b){return a/b}',
 return !1;return !0}',
         );
 
+        // https://github.com/matthiasmullie/minify/issues/54
+        $tests[] = array(
+            'function a() {
+  if (true)
+    return
+  if (false)
+    return
+}',
+            'function a(){if(!0)
+return
+if(!1)
+return}',
+        );
+
         return $tests;
     }
 }