Fix #604 Multiline Strings Forcefully Wrapping With Concatenation Causing Issues

[jdyjjj]

In this issue, for example, We use the code bellow

MethodSpec.methodBuilder().addComment("Test: $S", "foo\nbar");

the output in the past is that:

// Test: "foo"
    "bar"

now after my pull request, the outputs are like this:

// Test: "foo\nbar"

As you can see, I solve this issue.