config/core.txt: fix minor issues for `core.sparseCheckoutCone`

The sparse checkout feature can be used in "cone mode" or "non-cone
mode". In this one instance in the documentation, we refer to the latter
as "non cone mode" with whitespace rather than a hyphen. Align this with
the rest of our documentation.

A few words later in the same paragraph, there's mention of "a more
flexible patterns". Drop that leading "a" to fix the grammar.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Acked-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/core.txt

@@ -707,8 +707,8 @@ core.sparseCheckout::
 core.sparseCheckoutCone::
 	Enables the "cone mode" of the sparse checkout feature. When the
 	sparse-checkout file contains a limited set of patterns, this
-	mode provides significant performance advantages. The "non
-	cone mode" can be requested to allow specifying a more flexible
+	mode provides significant performance advantages. The "non-cone
+	mode" can be requested to allow specifying more flexible
 	patterns by setting this variable to 'false'. See
 	linkgit:git-sparse-checkout[1] for more information.