oc_FR locale: Fix spelling of April (bug 25639)

Confirmed by CLDR and a native speaker: "abril" is more often used even
if "abrial" is also correct.  Both nominative (alt_mon) and genitive (mon)
cases are updated.

localedata/locales/oc_FR

@@ -110,7 +110,7 @@ abmon   "gen.";/
 alt_mon "geni<U00E8>r";/
         "febri<U00E8>r";/
         "mar<U00E7>";/
-        "abrial";/
+        "abril";/
         "mai";/
         "junh";/
         "julhet";/
@@ -122,7 +122,7 @@ alt_mon "geni<U00E8>r";/
 mon     "de geni<U00E8>r";/
         "de febri<U00E8>r";/
         "de mar<U00E7>";/
-        "d<U2019>abrial";/
+        "d<U2019>abril";/
         "de mai";/
         "de junh";/
         "de julhet";/