(Documentation) Improve documentation for interval switch parser

* The generated documentation didn't differentiate between
  parameterized nouns that need "an" versus "a" as their
  article. Since the value in question is definite, we can use "the"
  to avoid the incorrect grammar.

Issue #218+

src/Rose/CommandLine/IntervalParser.h

@@ -63,7 +63,7 @@ class IntervalParser: public Sawyer::CommandLine::ValueParser {
                 " and the word \"empty\" or an empty string represents the empty " + interval + "."
 
                 " When the " + interval + " is specified as a range, the first " + value + " must be less than or equal to"
-                " the second value. A " + value + " can be specified in decimal, hexadecimal (leading \"0x\"),"
+                " the second value. The " + value + " can be specified in decimal, hexadecimal (leading \"0x\"),"
                 " octal (leading \"0\"), or binary (leading \"0b\"). The upper " + value + " can be the word \"max\" when"
                 " appearing after a comma.");
     }