contrithanks.sh: use same grep pattern and -a flag as contributors.sh

scripts/contrithanks.sh

@@ -36,7 +36,7 @@ cat ./docs/THANKS
 
 (
 git log $start..HEAD | \
-egrep -i '(Author|Commit|by):' | \
+egrep -ai '(^Author|^Commit|by):' | \
 cut -d: -f2- | \
 cut '-d<' -f1 | \
 tr , '\012' | \
@@ -46,12 +46,12 @@ sed -e 's/^ //' -e 's/ $//g' -e 's/@users.noreply.github.com$/ on github/'
 # grep out the list of names from RELEASE-NOTES
 # split on ", "
 # remove leading white spaces
-grep "^  [^ (]" RELEASE-NOTES| \
+grep -a "^  [^ (]" RELEASE-NOTES| \
 sed 's/, */\n/g'| \
 sed 's/^ *//'
 
 )| \
 sed -f ./docs/THANKS-filter | \
-grep ' ' | \
+grep -a ' ' | \
 sort -fu | \
-grep -xvf ./docs/THANKS
+grep -axvf ./docs/THANKS