vget fixes

* refactor(tools): remove trailing spaces in vget.v

* refactor(tools): fix mix tabs and spaces

* fix(tools): vget should exit non-zero when call with invalid arguments

* refactor(tools): extract vmodules directory create and chdir logic

* feat(tools): add travis-ci check to vget

.travis.yml

@@ -87,3 +87,10 @@ script:
       git clone https://github.com/vlang/vid
       cd vid && ../v -debug -o vid .
     fi
+  - |
+    if [[ "${TRAVIS_OS_NAME}" != "windows" ]]; then
+      v install nedpals.args
+      # ensure nedpals.args is installed
+      [[ -d ~/.vmodules/nedpals/args]]
+      git remote -v | grep 'https://github.com/nedpals/v-args (fetch)'
+    fi

tools/vget.v

@@ -18,19 +18,33 @@ struct Mod {
 	nr_downloads int
 }
 
-fn main() {
-	if os.args.len <= 1 {
-		println('usage: vget module [module] [module] [...]')
-		return
+fn get_vmodules_dir_path() string {
+	home := os.home_dir()
+
+	return '${home}.vmodules'
 }
 
-	home := os.home_dir()
-	home_vmodules := '${home}.vmodules'
+fn ensure_vmodules_dir_exist() {
+	home_vmodules := get_vmodules_dir_path()
+
 	if !os.dir_exists( home_vmodules ) {
 		println('Creating $home_vmodules/ ...')
 		os.mkdir(home_vmodules)
 	}
-	os.chdir(home_vmodules)
+}
+
+fn change_to_vmodules_dir() {
+	os.chdir(get_vmodules_dir_path())
+}
+
+fn main() {
+	if os.args.len <= 1 {
+		println('usage: vget module [module] [module] [...]')
+		exit(2)
+	}
+
+	ensure_vmodules_dir_exist()
+	change_to_vmodules_dir()
 
 	mut errors := 0
 	names := os.args.slice(1, os.args.len)
@@ -64,7 +78,7 @@ fn main() {
 			continue
 		}
 
-		final_module_path := '$home_vmodules/' + mod.name.replace('.', '/')
+		final_module_path := get_vmodules_dir_path() + '/' + mod.name.replace('.', '/')
 
 		println('Installing module "$name" from $mod.url to $final_module_path ...')
 		_ = os.exec('git clone --depth=1 $mod.url $final_module_path') or {