Empty line when opening terminal

Bug Report

Current Behavior

When add_line is enabled a new line is added at the beginning of every new terminal window/tab.

Expected Behavior

Using add_line should not add a new line above the first line of every window / tab.

Additional context/Screenshots

Environment

• Starship version: starship 0.25.0
• Shell type: zsh
• Shell version: zsh 5.3 (x86_64-apple-darwin18.0)
• Shell plugin manager: antibody
• Terminal emulator: iTerm2
• Operating system: OSX 10.14.6

Relevant Shell Configuration

eval "$(starship init zsh)"

source <(antibody init)
antibody bundle < ~/.zsh_plugins.txt

Starship Configuration

add_newline = true

Possible Solution

if config.add_newline {
        writeln!(buf).unwrap();
}

The above if-statement from https://github.com/starship/starship/blob/master/src/print.rs#L23 could be changed into something inspired by Spaceship's solution: https://github.com/maximbaz/spaceship-prompt/commit/815b68c70f21c5512765c87985897b98b8ed232c found in https://github.com/denysdovhan/spaceship-prompt/issues/462