build: update to latest canary version of MDC

Updates to the latest canary version of MDC so that we can
test the pointer changes to the testbed harness environment.

MDC recently changed the MDC slider to rely on pointer events
if available. Previously they just relied on mousedown/up events.

Author: devversion

package.json

@@ -58,7 +58,7 @@
     "@types/youtube": "^0.0.38",
     "@webcomponents/custom-elements": "^1.1.0",
     "core-js": "^2.6.9",
-    "material-components-web": "6.0.0-canary.deda86d8c.0",
+    "material-components-web": "7.0.0-canary.af71cfdd6.0",
     "rxjs": "^6.5.3",
     "systemjs": "0.19.43",
     "tslib": "^1.10.0",