Add dev paths to PATH and NU_LIB_DIRS in toolkit (#65)

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## Description
<!-- describe in a few words the changes -->

toolkit.nu

@@ -3,7 +3,12 @@ export-env {
     $env.NUPM_CACHE = ($env.FILE_PWD | path join _nupm_dev cache)
     $env.NUPM_TEMP = ($env.FILE_PWD | path join _nupm_dev tmp)
 
+    $env.PATH ++= [($env.FILE_PWD | path join _nupm_dev scripts)]
+    $env.NU_LIB_DIRS ++= [($env.FILE_PWD | path join _nupm_dev modules)]
+
     print $'NUPM_HOME:  ($env.NUPM_HOME)'
     print $'NUPM_CACHE: ($env.NUPM_CACHE)'
     print $'NUPM_TEMP:  ($env.NUPM_TEMP)'
+    print $'PATH: ($env.PATH)'
+    print $'NU_LIB_DIRS: ($env.NU_LIB_DIRS)'
 }