Fix home dir substitution

See the discussions in 953e422bed (commitcomment-58148656) . Tested with bash 5.1 and  bash 3.2

themes/powerline/powerline.base.bash

@@ -142,7 +142,7 @@ function __powerline_scm_prompt() {
 }
 
 function __powerline_cwd_prompt() {
-	local cwd="${PWD/$HOME/~}"
+	local cwd=${PWD/$HOME/\~}
 
 	echo "${cwd}|${CWD_THEME_PROMPT_COLOR}"
 }