Update Solomon Islands Pidgin (pis) autonym (#373)

Make it less ambiguous, so that it will be clearly distinct
from other pidgin languages, and findable by country
name.

This name is used, for example, here:
Beimers, Gerry (2009). Pijin: A Grammar of Solomon Islands Pidgin
(PhD thesis). The University of New England. page 26

And can also easily be found in many other sources.

data/language-data.json

@@ -3718,7 +3718,7 @@
             [
                 "PA"
             ],
-            "Pijin"
+            "Solomon Aelan Pijin"
         ],
         "piu": [
             "Latn",