fix: improve old termux version compatibility

[eatradish]

No description provided.

[MingcongBai]

This should lower Termux version requirement to v0.106-17-ge03858f0.

commit e03858f0659c108f12d44b5c162586a66d351765
Author: Leonid Pliushch <[email protected]>
Date:   Wed Feb 3 22:39:13 2021 +0200

    export app version in environment variable

diff --git a/app/src/main/java/com/termux/app/BackgroundJob.java b/app/src/main/java/com/termux/app/BackgroundJob.java
index 3df10026..cfb11cd4 100644
--- a/app/src/main/java/com/termux/app/BackgroundJob.java
+++ b/app/src/main/java/com/termux/app/BackgroundJob.java
@@ -6,6 +6,8 @@ import android.content.Intent;
 import android.os.Bundle;
 import android.util.Log;
 
+import com.termux.BuildConfig;
+
 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
@@ -138,6 +140,7 @@ public final class BackgroundJob {
 
         List<String> environment = new ArrayList<>();
 
+        environment.add("TERMUX_VERSION=" + BuildConfig.VERSION_NAME);
         environment.add("TERM=xterm-256color");
         environment.add("COLORTERM=truecolor");
         environment.add("HOME=" + TermuxService.HOME_PATH);