chore: fix .lintr config (#410)

.lintr

@@ -1,10 +1,10 @@
-linters: with_defaults(
-    # lintr defaults: https://github.com/jimhester/lintr#available-linters
+linters: linters_with_defaults(
+    # lintr defaults: https://lintr.r-lib.org/reference/default_linters.html
     # the following setup changes/removes certain linters
     assignment_linter = NULL, # do not force using <- for assignments
     object_name_linter = object_name_linter(c("snake_case", "CamelCase")), # only allow snake case and camel case object names
     cyclocomp_linter = NULL, # do not check function complexity
     commented_code_linter = NULL, # allow code in comments
-    line_length_linter = line_length_linter(120)
+    line_length_linter = line_length_linter(120L)
     )