Read Robolectric version from environment

app/build.gradle

@@ -14,6 +14,7 @@ android {
 
         buildConfigField "Integer", "databaseVersion", "19"
         buildConfigField "String", "databaseFilename", "\"uhabits.db\""
+        buildConfigField "Integer", "roboSdk", (System.getenv("ROBO_SDK")?: "25")
 
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
         testInstrumentationRunnerArgument "size", "medium"

app/src/test/java/org/isoron/uhabits/activities/BaseActivityTest.java

@@ -42,7 +42,7 @@ import static org.robolectric.Robolectric.*;
 import static org.robolectric.Shadows.*;
 
 @RunWith(RobolectricTestRunner.class)
-@Config(constants = BuildConfig.class)
+@Config(sdk = BuildConfig.roboSdk, constants = BuildConfig.class)
 public class BaseActivityTest
 {
     private static boolean hasCrashed = false;

app/src/test/java/org/isoron/uhabits/activities/BaseScreenTest.java

@@ -42,7 +42,7 @@ import static org.mockito.Mockito.*;
 import static org.robolectric.Robolectric.*;
 
 @RunWith(RobolectricTestRunner.class)
-@Config(constants = BuildConfig.class)
+@Config(sdk = BuildConfig.roboSdk, constants = BuildConfig.class)
 public class BaseScreenTest
 {
     @Test