Support rust 1.51.0 (#789)

src/steps/os/dragonfly.rs

@@ -10,7 +10,7 @@ pub fn upgrade_packages(sudo: Option<&PathBuf>, run_type: RunType) -> Result<()>
     print_separator("DrgaonFly BSD Packages");
     run_type
         .execute(sudo)
-        .args(["/usr/local/sbin/pkg", "upgrade"])
+        .args(&["/usr/local/sbin/pkg", "upgrade"])
         .check_run()
 }
 
@@ -18,7 +18,7 @@ pub fn audit_packages(sudo: &Option<PathBuf>) -> Result<()> {
     if let Some(sudo) = sudo {
         println!();
         Command::new(sudo)
-            .args(["/usr/local/sbin/pkg", "audit", "-Fr"])
+            .args(&["/usr/local/sbin/pkg", "audit", "-Fr"])
             .spawn()?
             .wait()?;
     }