dib-lint: make it work on Mac OS X

Pass an explicit template to mktemp since that is required on Mac OS X.
Hardcoded to /tmp since I did not want to bother validating TMPDIR which
is user supplied.

Explicit define a repeating group which causes a grep error:
    repetition-operator operand invalid

Change-Id: Ib23cc15db7f7dfdd611280884e46342562d545df

bin/dib-lint

@@ -59,7 +59,7 @@ error() {
 }
 
 rc=0
-TMPDIR=$(mktemp -d)
+TMPDIR=$(mktemp -d /tmp/tmp.XXXXXXXXXX)
 trap "rm -rf $TMPDIR" EXIT
 for i in $(find elements -type f \
                 -not -name \*~ \
@@ -80,7 +80,7 @@ for i in $(find elements -type f \
             flake8 $i
         else
             if ! excluded indent ; then
-                if grep -q "^ \{4\}* \{1,3\}[^ ]" ${i}; then
+                if grep -q "^\( \{4\}\)* \{1,3\}[^ ]" ${i}; then
                     error "$i should use 4 spaces indent"
                 fi
             fi