shellcheck: Fix SC2006 issue

See,

$ find . -name "*.sh" | xargs shellcheck -i SC2006

In ./roll-tarballs.sh line 62:
    echo "HEAD (on branch `git rev-parse --abbrev-ref HEAD`)"
                          ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean:
    echo "HEAD (on branch $(git rev-parse --abbrev-ref HEAD))"

In ./nx-X11/x-indent-all.sh line 2:
where=`dirname $0`
      ^----------^ SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean:
where=$(dirname $0)

In ./nx-X11/x-indent.sh line 5:
INDENT=`which gnuindent || which gindent || which indent`
       ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.

Did you mean:
INDENT=$(which gnuindent || which gindent || which indent)

For more information:
  https://www.shellcheck.net/wiki/SC2006 -- Use $(...) notation instead of le...

Signed-off-by: Mario Trangoni <mjtrangoni@gmail.com>

3 files changed, 3 insertions, 3 deletions

diff --git a/nx-X11/x-indent-all.sh b/nx-X11/x-indent-all.sh
index 6addaf400..d3c4113de 100755
--- a/nx-X11/x-indent-all.sh
+++ b/nx-X11/x-indent-all.sh
@@ -1,4 +1,4 @@
 #!/bin/sh
-where=`dirname $0`
+where=$(dirname $0)
 git ls-files | grep '\.[chm]$' | xargs sh "$where"/x-indent.sh
 
diff --git a/nx-X11/x-indent.sh b/nx-X11/x-indent.sh
index e662cce09..327aa6a4f 100755
--- a/nx-X11/x-indent.sh
+++ b/nx-X11/x-indent.sh
@@ -2,7 +2,7 @@
 
 # We want GNU indent, so first search for gindent to avoid /usr/bin/indent
 # on the BSDs, which won't work for us
-INDENT=`which gnuindent || which gindent || which indent`
+INDENT=$(which gnuindent || which gindent || which indent)
 
 if [ -z "${INDENT}" ] ; then
     echo "Could not find indent, sorry..." >&2
diff --git a/roll-tarballs.sh b/roll-tarballs.sh
index dc30a8a17..acef42daa 100755
--- a/roll-tarballs.sh
+++ b/roll-tarballs.sh
@@ -59,7 +59,7 @@ fi
 if ! git rev-parse --verify -q "$CHECKOUT" >/dev/null; then
     echo "   '${RELEASE}' is not a valid release number because there is no git tag named ${CHECKOUT}."
     echo "   Please specify one of the following releases:"
-    echo "HEAD (on branch `git rev-parse --abbrev-ref HEAD`)"
+    echo "HEAD (on branch $(git rev-parse --abbrev-ref HEAD))"
     git tag -l | grep "^redist" | cut -f2 -d"/" | sort -u
     exit 1
 fi