MappingsPoet crash when handling class named "package-info"

[thecatcore]

Discovered while creating mappings for 18w19a, which contains two deobfuscated package-info files.

Error: Exception in thread "main" java.lang.IllegalArgumentException: not a valid name: package-info
    at com.squareup.javapoet.Util.checkArgument(Util.java:53)
    at com.squareup.javapoet.TypeSpec$Builder.<init>(TypeSpec.java:502)
    at com.squareup.javapoet.TypeSpec$Builder.<init>(TypeSpec.java:475)
    at com.squareup.javapoet.TypeSpec.interfaceBuilder(TypeSpec.java:148)
    at com.squareup.javapoet.TypeSpec.interfaceBuilder(TypeSpec.java:152)
    at net.fabricmc.mappingpoet.ClassBuilder.setupBuilder(ClassBuilder.java:156)
    at net.fabricmc.mappingpoet.ClassBuilder.<init>(ClassBuilder.java:86)
    at net.fabricmc.mappingpoet.Main.writeClass(Main.java:242)
    at net.fabricmc.mappingpoet.Main.lambda$generate$0(Main.java:95)
    at net.fabricmc.mappingpoet.Main.lambda$forEachClass$5(Main.java:171)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at net.fabricmc.mappingpoet.Main.forEachClass(Main.java:171)
    at net.fabricmc.mappingpoet.Main.generate(Main.java:95)
    at net.fabricmc.mappingpoet.Main.main(Main.java:89)