docs: Correct “webapp” to “web app”.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

docs/testing/philosophy.md

@@ -141,7 +141,7 @@ Some examples of this philosophy:
   run, and produce this output".
 
 In the Zulip context:
-* Zulip uses the same API for our webapp as for our mobile clients and
+* Zulip uses the same API for our web app as for our mobile clients and
   third-party API clients, and most of our server tests are written
   against the Zulip API.
 * The tests for Zulip's incoming webhooks work by sending actual

docs/testing/testing-with-puppeteer.md

@@ -28,7 +28,7 @@ The Puppeteer tests use a real Chromium browser (powered by
 [puppeteer](https://github.com/puppeteer/puppeteer)), connected to a
 real Zulip development server.  These are black-box tests: Steps in a
 Puppeteer test are largely things one might do as a user of the Zulip
-webapp, like "Type this key", "Wait until this HTML element
+web app, like "Type this key", "Wait until this HTML element
 appears/disappears", or "Click on this HTML element".
 
 For example, this function might test the `x` keyboard shortcut to

docs/testing/testing.md

@@ -3,7 +3,7 @@
 Zulip takes pride in its extensive, carefully designed test suites.
 For example, `test-backend` runs a complete test suite (~98% test
 coverage; 100% on core code) for the Zulip server in under a minute on
-a fast laptop; very few webapps of similar scope can say something
+a fast laptop; very few web apps of similar scope can say something
 similar.
 
 This page focused on the mechanics of running automated tests in a