ci: update wabt to 1.0.15

Author: gumb0

circle.yml

@@ -184,7 +184,7 @@ jobs:
     - run:
         name: "Install wabt"
         working_directory: ~/bin
-        command: curl -L https://github.com/WebAssembly/wabt/releases/download/1.0.13/wabt-1.0.13-linux.tar.gz | tar xz --strip=1
+        command: curl -L https://github.com/WebAssembly/wabt/releases/download/1.0.15/wabt-1.0.15-linux.tar.gz | tar xz --strip=1
     - run:
         name: "Check wat2wasm4cpp"
         command: |