fix wording of spec description [ci skip]

spec/ruby/language/source_encoding_spec.rb

@@ -15,7 +15,7 @@ describe "Source files" do
   end
 
   describe "encoded in UTF-16 LE without a BOM" do
-    it "are parsed because empty as they contain a NUL byte before the encoding comment" do
+    it "are parsed as empty because they contain a NUL byte before the encoding comment" do
       ruby_exe(fixture(__FILE__, "utf16-le-nobom.rb"), args: "2>&1").should == ""
     end
   end