Fix backquotes in iOS docs.

Change-Id: Icd0ef4dbaabc1f312e195cb79cf7f2aa517cb592
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/842657
Auto-Submit: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
diff --git a/site/docs/user/build.md b/site/docs/user/build.md
index bc010d5..79ed47c 100644
--- a/site/docs/user/build.md
+++ b/site/docs/user/build.md
@@ -294,7 +294,7 @@
 
 By default this will also package (and for non-simulator devices, sign) iOS test binaries.
 If you wish to skip signing (for testing compilation alone, for example), you can disable it by
-setting 'skia_ios_use_signing' to 'false'.
+setting `skia_ios_use_signing` to `false`.
 
 When signing, the build defaults to a Google signing identity and provisioning profile.
 To use a different one