scalar: fix command documentation section header

Rename the last section header in 'contrib/scalar/scalar.txt' from "Scalar"
to "GIT". The linting rules of the 'documentation' CI build enforce the
existence of a "GIT" section in command documentation. Although 'scalar.txt'
is not yet checked, it will be in a future patch.

Here, changing the header name is more appropriate than making a
Scalar-specific exception to the linting rule. The existing "Scalar" section
contains only a link back to the main Git documentation, essentially the
same as the "GIT" section in builtin documentation. Changing the section
name further clarifies the Scalar-Git association and maintains consistency
with the rest of Git.

Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/scalar/scalar.txt

@@ -161,6 +161,6 @@ SEE ALSO
 --------
 linkgit:git-clone[1], linkgit:git-maintenance[1].
 
-Scalar
+GIT
 ---
-Associated with the linkgit:git[1] suite
+Part of the linkgit:git[1] suite