BUG: Pin preact and friends using ~ rather than ^. (jupyter#4681)

The most recent release of preact-compat appears to have broken notebook.

Author: Scott Sanderson

bower.json

@@ -16,9 +16,9 @@
     "marked": "~0.4",
     "MathJax": "^2.7.4",
     "moment": "~2.19.3",
-    "preact": "https://unpkg.com/preact@^7.2.0/dist/preact.min.js",
-    "preact-compat": "https://unpkg.com/preact-compat@^3.14.3/dist/preact-compat.min.js",
-    "proptypes": "https://unpkg.com/proptypes@^0.14.4/index.js",
+    "preact": "https://unpkg.com/preact@~7.2.0/dist/preact.min.js",
+    "preact-compat": "https://unpkg.com/preact-compat@~3.14.3/dist/preact-compat.min.js",
+    "proptypes": "https://unpkg.com/proptypes@~0.14.4/index.js",
     "requirejs": "~2.2",
     "requirejs-text": "~2.0.15",
     "requirejs-plugins": "~1.0.3",