Update rbenv module (#1007)

heres the changes

- Removed outdated code
- Replaced the old load-env with $env assignment
- Kept the rbenv command intact but focused on the "rbenv shell"
(modified a subcommand rather than the whole command)
- Deleted unused command completions

modules/rbenv/README.md

@@ -4,7 +4,7 @@ This script provides minimal working rbenv setup.
 It can be used by importing its exported commands via:
 
 ```
-use path/to/rbenv.nu *
+use path/to/rbenv.nu
 ```
 
 With `path/to` being either the relative path of the file to your current working directory or its absolute path. 

modules/rbenv/rbenv.nu

@@ -1,38 +1,19 @@
 # rbenv
-export-env {
-    load-env {
-        PATH: ($env.PATH | split row (char esep) | prepend [$"($env.HOME)/.rbenv/bin" $"($env.HOME)/.rbenv/shims"])
-        RBENV_VERSION: ""
-        RBENV_VERSION_OLD: ""
-        RBENV_SHELL: "nu"
-    }
+export-env { 
+    use std/util "path add"
+
+    $env.RBENV_SHELL = 'nu'
+    $env.RBENV_VERSION = ''
+    path add $"($env.HOME)/.rbenv/bin"
+    path add $"($env.HOME)/.rbenv/shims"
 }
 
-export def --env main [
-	command?: string@'nu-complete rbenv',
-	...args
-] {
-    let new_env = if $command in ["rehash", "shell"] {
-        # implement each on indiviudaly e.g.
-        if $command == "shell" {
-            { RBENV_VERSION_OLD: $env.RBENV_VERSION RBENV_VERSION: $args.0 }
-        } else {
-            error make { msg: $"`($command)` command is not supported yet" }
-        }
+export def --env "shell" [version: string] {
+    let run = (^rbenv sh-shell $version | complete)
+    if ($run.exit_code == 0) {
+        $env.RBENV_VERSION_OLD = ($env.RBENV_VERSION | default "")
+        $env.RBENV_VERSION = $version
     } else {
-    	if ($command | is-empty) {
-    		^rbenv
-    	} else {
-        	^rbenv $command $args
-    	}
-        {}
+        print -e $run.stderr
     }
-    load-env $new_env
-}
-
-def 'nu-complete rbenv' [] {
-    ^rbenv help
-    | lines
-    | where ($it | str starts-with "   ")
-    | each {|entry| $entry | split row ' ' | get 0 }
 }