Accept custom directories in the bump script (kanisterio#734)

* Accept custom directories in the bump script.

* To grep the version (0.35.0) we used the regex using -E flag
that means . would imply to any character and that was the
reason we were seeing some unexpected behaviour.
This changes the flag to -F that matches the exact word.

* Improve comment

Co-authored-by: Vivek Singh <vsingh.ggits.2010@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

build/bump_version.sh

@@ -25,10 +25,15 @@ usage() {
 }
 
 main() {
-    local prev=${1:?"$(usage)"}
-    local next=${2:?"$(usage)"}
-    local -a pkgs=(docker/ scripts/ examples/ pkg/ helm/)
-    grep -E "${prev}" -r  "${pkgs[@]}" | cut -d ':' -f 1 | uniq | xargs sed -ri "s/${prev}/${next//./\\.}/g"
+    local prev=${1:?"$(usage)"}; shift
+    local next=${1:?"$(usage)"}; shift
+    if [ "$#" -eq 0 ]; then
+            pkgs=( docker/ scripts/ examples/ pkg/ helm/ )
+        else
+            pkgs=( "$@" )
+    fi
+    # -F matches for exact words, not regular expression (-E), that is what required here
+    grep -F "${prev}" -r  "${pkgs[@]}" | cut -d ':' -f 1 | uniq | xargs sed -ri "s/${prev}/${next//./\\.}/g"
 }
 
 main $@