doc: Match text to the struct name (#217)

Author: vreuter

lib/csv.rb

@@ -513,7 +513,7 @@
 #  [" 1 ", #<struct CSV::FieldInfo index=1, line=2, header=nil>]
 #  [" baz ", #<struct CSV::FieldInfo index=0, line=3, header=nil>]
 #  [" 2 ", #<struct CSV::FieldInfo index=1, line=3, header=nil>]
-# Each CSV::Info object shows:
+# Each CSV::FieldInfo object shows:
 # - The 0-based field index.
 # - The 1-based line index.
 # - The field header, if any.