style(shell): improve shell script formatting and quoting

Apply shfmt formatting and fix some schellcheck complaints.

libexec/tmuxifier-tmux-version

@@ -19,16 +19,16 @@ fi
 
 # The vercomp() function is shamelessly ripped/borrowed from the following
 # StackOverflow answer: http://stackoverflow.com/a/4025065/42146
-vercomp () {
+vercomp() {
   if [[ $1 == $2 ]]; then return 0; fi
 
   local IFS=.
   local i ver1=($1) ver2=($2)
 
   # fill empty fields in ver1 with zeros
-  for ((i=${#ver1[@]}; i<${#ver2[@]}; i++)); do ver1[i]=0; done
+  for ((i = ${#ver1[@]}; i < ${#ver2[@]}; i++)); do ver1[i]=0; done
 
-  for ((i=0; i<${#ver1[@]}; i++)); do
+  for ((i = 0; i < ${#ver1[@]}; i++)); do
     # fill empty fields in ver2 with zeros
     if [[ -z ${ver2[i]} ]]; then ver2[i]=0; fi
 
@@ -63,8 +63,8 @@ else
 
   vercomp "$version" "$1"
   case $? in
-    0) echo '=';;
-    1) echo '>';;
-    2) echo '<';;
+    0) echo '=' ;;
+    1) echo '>' ;;
+    2) echo '<' ;;
   esac
 fi