S3 diagnostics suggests correction with typo

[sven-stodtmann]

When missing @exportS3Method, I get the following, potentially very helpful message:
S3 method method.cls needs @export or @exportS3method tag.
However, when copy-pasting the suggestion, it leads to an error since "method" must be capitalized.
It should be
S3 method method.cls needs @export or @exportS3Method tag.
instead.