build: hardcode versionCode for F-Droid compatibility

Author: potatameister

android/app/build.gradle

@@ -7,7 +7,7 @@ android {
         applicationId "com.paperknife.app"
         minSdkVersion rootProject.ext.minSdkVersion
         targetSdkVersion rootProject.ext.targetSdkVersion
-        versionCode System.getenv("ANDROID_VERSION_CODE") ? System.getenv("ANDROID_VERSION_CODE").toInteger() : 10
+        versionCode 100
         versionName "1.0.0"
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         aaptOptions {