/usr/share/gocode/src/golang.org/x/text/cases/ is in golang-golang-x-text-dev 0.0~git20170627.0.6353ef0-1ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/gocode/src/golang.org/x/text/cases/cases.go
/usr/share/gocode/src/golang.org/x/text/cases/context.go
/usr/share/gocode/src/golang.org/x/text/cases/context_test.go
/usr/share/gocode/src/golang.org/x/text/cases/example_test.go
/usr/share/gocode/src/golang.org/x/text/cases/fold.go
/usr/share/gocode/src/golang.org/x/text/cases/fold_test.go
/usr/share/gocode/src/golang.org/x/text/cases/gen.go
/usr/share/gocode/src/golang.org/x/text/cases/gen_trieval.go
/usr/share/gocode/src/golang.org/x/text/cases/icu.go
/usr/share/gocode/src/golang.org/x/text/cases/icu_test.go
/usr/share/gocode/src/golang.org/x/text/cases/info.go
/usr/share/gocode/src/golang.org/x/text/cases/map.go
/usr/share/gocode/src/golang.org/x/text/cases/map_test.go
/usr/share/gocode/src/golang.org/x/text/cases/tables.go
/usr/share/gocode/src/golang.org/x/text/cases/tables_test.go
/usr/share/gocode/src/golang.org/x/text/cases/trieval.go