Support .s extension

package.json

@@ -26,7 +26,7 @@
         "languages": [{
             "id": "riscv",
             "aliases": ["RISC-V Assembly", "riscv"],
-            "extensions": [".riscv"],
+            "extensions": [".riscv", ".s"],
             "configuration": "./configurations/riscv.configuration.json"
         }],
         "grammars": [{
@@ -35,4 +35,4 @@
             "path": "./syntaxes/riscv.tmLanguage.json"
         }]
     }
-}
+}