update usage of SUDO_ASKPASS -> NH_SUDO_ASKPASS

with reference to
#261 (comment)

Author: dvishal485

src/commands.rs

@@ -83,8 +83,8 @@ impl Command {
                 Exec::cmd("sudo")
             };
 
-            // use SUDO_ASKPASS program for sudo if present
-            let cmd = if std::env::var("SUDO_ASKPASS").is_ok() {
+            // use NH_SUDO_ASKPASS program for sudo if present
+            let cmd = if std::env::var("NH_SUDO_ASKPASS").is_ok() {
                 cmd.arg("-A")
             } else {
                 cmd

src/main.rs

@@ -55,8 +55,8 @@ fn self_elevate() -> ! {
     use std::os::unix::process::CommandExt;
 
     let mut cmd = std::process::Command::new("sudo");
-    // use SUDO_ASKPASS program for sudo if present
-    if std::env::var("SUDO_ASKPASS").is_ok() {
+    // use NH_SUDO_ASKPASS program for sudo if present
+    if std::env::var("NH_SUDO_ASKPASS").is_ok() {
         cmd.arg("-A");
     }