Running `PlugUpgrade` in Neovim's `--headless` mode has (mildly) malformed output

[eliminmax]

Explain the problem here ... Running nvim --headless -c 'PlugUpgrade' -c qa results in the output Downloading the latest version of vim-plugvim-plug is already up-to-date with no newline in between the messages or at the end, resulting in the following output:

---

NVIM v0.4.4
Build type: Release
Lua 5.1
Compilation: /usr/bin/cc -g -O2 -fdebug-prefix-map=/build/neovim-AMNr6D/neovim-0.4.4=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=1 -DDISABLE_LOG -Wdate-time -D_FORTIFY_SOURCE=1 -O2 -DNDEBUG -DMIN_LOG_LEVEL=3 -Wall -Wextra -pedantic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wshadow -Wconversion -Wmissing-prototypes -Wimplicit-fallthrough -Wvla -fstack-protector-strong -fno-common -fdiagnostics-color=always -DINCLUDE_GENERATED_DECLARATIONS -D_GNU_SOURCE -DNVIM_MSGPACK_HAS_FLOAT32 -DNVIM_UNIBI_HAS_VAR_FROM -I/build/neovim-AMNr6D/neovim-0.4.4/build/config -I/build/neovim-AMNr6D/neovim-0.4.4/src -I/usr/include -I/usr/include/lua5.1 -I/build/neovim-AMNr6D/neovim-0.4.4/build/src/nvim/auto -I/build/neovim-AMNr6D/neovim-0.4.4/build/include
Compiled by team+vim@tracker.debian.org

Features: +acl +iconv +tui
See ":help feature-compile"

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/usr/share/nvim"

Run :checkhealth for more info

• Type:
  • [x] Bug
  • [ ] Enhancement
  • [ ] Feature Request
  • [ ] Question
• OS:
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  • [ ] OS X
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• Vim:
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  • [x] Neovim