Correctly set PATH inside and outside of TMUX

I noticed my `PATH` had duplicated entries in it. With help from a
GitHub issue[1] and a comment[2] linking to another comment at
StackOverflow[3] I understand the reason behind this duplication and it
also provided me with a solution.

[1]: rbenv/rbenv#369
[2]: rbenv/rbenv#369 (comment)
[3]: https://superuser.com/questions/544989/does-tmux-sort-the-path-variable/583502#583502

.bash_profile

@@ -1,6 +1,14 @@
-[[ -s ~/.bashrc ]] && source ~/.bashrc
+if [ -f /etc/profile ]; then
+    PATH=""
+    source /etc/profile
+fi
+
+. ~/.profile
+. ~/.bashrc
 [[ -s ~/.bash_config ]] && source ~/.bash_config
 
+export PATH="$HOME/.cargo/bin:$PATH"
+
 alias h='cd'
 alias g='git'
 alias gs='git status'
@@ -40,5 +48,3 @@ export FZF_DEFAULT_OPTS="--no-mouse --height 50% -1 --reverse --multi --inline-i
 export FZF_DEFAULT_COMMAND='rg --files --hidden --glob !.git'
 
 test -e "${HOME}/.iterm2_shell_integration.bash" && source "${HOME}/.iterm2_shell_integration.bash"
-
-export PATH="$HOME/.cargo/bin:$PATH"