minor symfony#12449 fixed typo (ojhaujjwal)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes symfony#12449).

Discussion
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fixed typo

Commits
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a7c2a9a fixed typo

Author: fabpot

UPGRADE-3.0.md

@@ -8,8 +8,8 @@ UPGRADE FROM 2.x to 3.0
 
       * `registerNamespaces()` -> `addPrefixes()`
       * `registerPrefixes()` -> `addPrefixes()`
-      * `registerNamespaces()` -> `addPrefix()`
-      * `registerPrefixes()` -> `addPrefix()`
+      * `registerNamespace()` -> `addPrefix()`
+      * `registerPrefix()` -> `addPrefix()`
       * `getNamespaces()` -> `getPrefixes()`
       * `getNamespaceFallbacks()` -> `getFallbackDirs()`
       * `getPrefixFallbacks()` -> `getFallbackDirs()`