Update Android Dependencies Docs (#3438)

I was unable to compile because I use multidex and this line of code force the multidex library to be version 25.4.0 when the latest for this one is 1.0.3. This little fix may save a lot headaches.

docs/docs/Installing.md

@@ -207,7 +207,7 @@ android {
 configurations.all {
     resolutionStrategy.eachDependency { DependencyResolveDetails details ->
         def requested = details.requested
-        if (requested.group == 'com.android.support') {
+        if (requested.group == 'com.android.support' && requested.name != 'multidex') {
             details.useVersion "25.4.0" // <- Change this to whatever version you're using
         }
     }
@@ -219,4 +219,4 @@ dependencies {
     implementation 'com.android.support:appcompat-v7:25.4.0'
 }
 
-```
+```