Fix `18+` false positives with NSFW check (#279)

Was noticing false positives with our test room names like: `planet-1688081266353-room-18`

Before:
```regex
/(\b|_)18+(\b|_)/i
```

After:
```regex
/(\b|_|-|\s|^)18\+(\b|_|-|\s|$)/i
```

shared/lib/check-text-for-nsfw.js

@@ -1,7 +1,13 @@
 'use strict';
 
+const escapeStringRegexp = require('escape-string-regexp');
+
 const NSFW_WORDS = ['nsfw', 'porn', 'nudes', 'sex', '18+'];
-const NSFW_REGEXES = NSFW_WORDS.map((word) => new RegExp(`(\\b|_)${word}(\\b|_)`, 'i'));
+const NSFW_REGEXES = NSFW_WORDS.map(
+  // We use `(\b|_|-|\s|^)` instead of just `(\b|_)` because the word boundary doesn't
+  // match next to the `+` sign in `18+`
+  (word) => new RegExp(`(\\b|_|-|\\s|^)${escapeStringRegexp(word)}(\\b|_|-|\\s|$)`, 'i')
+);
 
 // A very basic check for NSFW content that just looks for some keywords in the given
 // text

test/shared/lib/check-text-for-nsfw-tests.js

@@ -13,6 +13,11 @@ describe('checkTextForNsfw', () => {
     NSFW_foo: true,
     'NSFW-foo': true,
     'NSFW:foo': true,
+    '18+ only': true,
+    // Previous false positives that we ran into in the wild that should not be flagged
+    // as NSFW
+    '1888-great-blizzard': false,
+    'argon-18-element': false,
   }).forEach(([inputText, expectedNsfw]) => {
     it(`should return ${expectedNsfw} for '${inputText}'`, () => {
       assert.strictEqual(