Increment x/wasm error codes by 1

[ethanfrey]

Closes #240

[codecov]

Codecov Report

Merging #276 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #276   +/-   ##
=======================================
  Coverage   74.30%   74.30%           
=======================================
  Files          27       27           
  Lines        2339     2339           
=======================================
  Hits         1738     1738           
  Misses        483      483           
  Partials      118      118           

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