tweak sndsgd/error dependency

ran into what _seems_ like a composer bug:
```
Problem 1
    - sndsgd/form 0.1.3 requires sndsgd/error ~0.0.3 -> satisfiable by sndsgd/error[0.0.4].
    - sndsgd/form dev-master requires sndsgd/error ~0.0.3 -> satisfiable by sndsgd/error[0.0.4].
    - Conclusion: don't install sndsgd/error 0.0.4
    - Installation request for sndsgd/form >=0.1.3 -> satisfiable by sndsgd/form[0.1.3, dev-master].
```

composer.json

@@ -18,7 +18,7 @@
     "require": {
         "php": ">=7.0.0",
         "sndsgd/util": ">=1.1.0",
-        "sndsgd/error": ">=0.0.4",
+        "sndsgd/error": "~0.0.4",
         "sndsgd/form": ">=0.1.3",
         "sndsgd/fs": ">=0.3.1"
     },