fix: set powerline env var

resolves #133

src/init/omp.bash

@@ -1,4 +1,5 @@
 export POSH_THEME=::CONFIG::
+export POWERLINE_COMMAND="oh-my-posh"
 
 TIMER_START="/tmp/${USER}.start.$$"
 

src/init/omp.fish

@@ -1,4 +1,5 @@
 set -g posh_theme ::CONFIG::
+set -g POWERLINE_COMMAND "oh-my-posh"
 
 function fish_prompt
     set -l omp_stack_count (count $dirstack)

src/init/omp.ps1

@@ -1,6 +1,7 @@
 # Powershell doesn't default to UTF8 just yet, so we're forcing it as there are too many problems
 # that pop up when we don't
 [console]::InputEncoding = [console]::OutputEncoding = New-Object System.Text.UTF8Encoding
+$env:POWERLINE_COMMAND = "oh-my-posh"
 
 $global:PoshSettings = New-Object -TypeName PSObject -Property @{
     Theme = "";

src/init/omp.zsh

@@ -1,4 +1,5 @@
 export POSH_THEME=::CONFIG::
+export POWERLINE_COMMAND="oh-my-posh"
 
 function omp_preexec() {
   omp_start_time=$(::OMP:: --millis)