BuildConfig: use build time instead of current time for timestamp

app/build.gradle

@@ -20,7 +20,7 @@ android {
         versionCode 86
         versionName "0.9.1.2"
 
-        buildConfigField "java.util.Date", "buildTime", "new java.util.Date()"
+        buildConfigField "long", "buildTime", System.currentTimeMillis() + "L"
     }
 
     buildTypes {

app/src/main/java/at/bitfire/davdroid/HttpClient.java

@@ -26,6 +26,7 @@ import java.io.IOException;
 import java.io.StringReader;
 import java.net.CookieManager;
 import java.text.SimpleDateFormat;
+import java.util.Date;
 import java.util.Locale;
 import java.util.concurrent.TimeUnit;
 
@@ -40,7 +41,7 @@ public class HttpClient extends OkHttpClient {
 
     static final String userAgent;
     static {
-        String date = new SimpleDateFormat("yyyy/MM/dd", Locale.US).format(BuildConfig.buildTime);
+        String date = new SimpleDateFormat("yyyy/MM/dd", Locale.US).format(new Date(BuildConfig.buildTime));
         userAgent = "DAVdroid/" + BuildConfig.VERSION_NAME + " (" + date + "; dav4android) Android/" + Build.VERSION.RELEASE;
     }
 

app/src/main/java/at/bitfire/davdroid/ui/DebugInfoActivity.java

@@ -34,6 +34,7 @@ import org.apache.commons.lang3.text.WordUtils;
 import java.io.File;
 import java.io.FileWriter;
 import java.io.IOException;
+import java.util.Date;
 
 import at.bitfire.dav4android.exception.HttpException;
 import at.bitfire.davdroid.BuildConfig;
@@ -191,7 +192,7 @@ public class DebugInfoActivity extends Activity implements LoaderManager.LoaderC
                 } catch(PackageManager.NameNotFoundException e) {}
                 report.append(
                         "SOFTWARE INFORMATION\n" +
-                                "DAVdroid version: " + BuildConfig.VERSION_NAME + " (" + BuildConfig.VERSION_CODE + ") " + BuildConfig.buildTime.toString() + "\n" +
+                                "DAVdroid version: " + BuildConfig.VERSION_NAME + " (" + BuildConfig.VERSION_CODE + ") " + new Date(BuildConfig.buildTime) + "\n" +
                                 "Installed from: " + installedFrom + "\n" +
                                 "JB Workaround installed: " + (workaroundInstalled ? "yes" : "no") + "\n\n"
                 );