Add Drush 10 and smart theme compilation

Enforcing this lets us do dynamic theme compilation per thinkshout/ts_recipes#14
Note that this is waiting on pantheon-systems/example-drops-8-composer#334 and km_collaborative to switch to that release.

composer.json

@@ -19,11 +19,12 @@
         }
     },
     "require": {
-        "united-philanthropy-forum/km_collaborative": ">=0.1.4"
+        "united-philanthropy-forum/km_collaborative": "dev-drush10"
     },
     "require-dev": {
         "dealerdirect/phpcodesniffer-composer-installer": ">=0.5.0",
         "dmore/behat-chrome-extension": ">=1.3",
+        "drush/drush": "^10",
         "drupal/coder": ">=8.3.1",
         "drupal/console": ">=1",
         "drupal/drupal-extension": ">=4.1",
@@ -76,7 +77,9 @@
         ],
         "compile-code": [
             "npm install --prefix web/profiles/contrib/km_collaborative/themes/kmc_base_theme",
-            "npm run build --prefix web/profiles/contrib/km_collaborative/themes/kmc_base_theme"
+            "npm run build --prefix web/profiles/contrib/km_collaborative/themes/kmc_base_theme",
+            "npm install --prefix=$(drush dd $(drush st --field=theme))",
+            "npm run build --prefix=$(drush dd $(drush st --field=theme))"
         ],
         "post-drupal-scaffold-cmd": [
             "chmod 755 .ci/build/multidev-save && chmod 755 .ci/deploy/pantheon/dev-multidev"