Fix line break removal before package directive

Due to an upstream bug[1] if `golines` were to reformat (i.e. it
actually found a line that was too long) a file with a block comment
before the package directive, the newline before the package directive
would be stripped, e.g.

    /*
    this is a comment
    */
    package foo

Would become

    /*
    this is a comment
    */ package foo

The underlying issue has been fixed upstream, so fix here by bumping the
version of `github.com/dave/dst` to include that fix. Here's a summary of
the changes in that package from the previously used version:

    $ git log --no-merges --format='%h %s' v0.27.0..v0.27.3
    5fa8d6e Fixes segmentio#69
    bc71a76 Upgrade golang.org/x/tools to v0.1.12
    b6f3447 decorator: make an error more verbose

[1] dave/dst#69

_fixtures/doc_comment_block.go

@@ -0,0 +1,4 @@
+/*
+This is a long package comment. It contains nothing interesting but is longer than the default line limit
+*/
+package fixtures

_fixtures/doc_comment_block__exp.go

@@ -0,0 +1,4 @@
+/*
+This is a long package comment. It contains nothing interesting but is longer than the default line limit
+*/
+package fixtures