title: Disable DexGuard only for certain product flavors
body: <p>I use DexGuard and have 4 product flavors (prod, qa, dev, mock) for 2 build types (release and debug) and I don't enable DexGuard for debug builds and hence I get 4 variants (<code>dexguardProdRelease</code>...<code>dexguardMockRelease</code>) however, I don't want to enable DexGuard for dev and mock flavors. </p>
  
  <p>I learnt about <code>variantFilter</code> that Gradle provides however, I don't know how to use that command in relation to a plugin, DexGuard, in this case.</p>