Run TypeScript tests

There aren't any yet, but I'm about to write a test and it's going
to be in TypeScript and I don't want to lump this change in with
a bunch of other stuff.

package.json

@@ -128,6 +128,7 @@
     "@types/classnames": "^2.2.10",
     "@types/counterpart": "^0.18.1",
     "@types/flux": "^3.1.9",
+    "@types/jest": "^26.0.20",
     "@types/linkifyjs": "^2.1.3",
     "@types/lodash": "^4.14.158",
     "@types/modernizr": "^3.5.3",
@@ -172,7 +173,7 @@
   "jest": {
     "testEnvironment": "./__test-utils__/environment.js",
     "testMatch": [
-      "<rootDir>/test/**/*-test.js"
+      "<rootDir>/test/**/*-test.[jt]s"
     ],
     "setupFiles": [
       "jest-canvas-mock"