install.sh and install.ps1 headers disagree on dash style

[joshrotenberg]

The two installer templates render the same header line differently:

priv/templates/install.sh.eex:2

# <%= @app %> installer — generated by tinfoil <%= @tinfoil_version %>

priv/templates/install.ps1.eex:1

# <%= @app %> installer -- generated by tinfoil <%= @tinfoil_version %>

One uses an em dash, the other an ASCII double hyphen. Rendered, from
joshrotenberg/hexpm-mcp:

scripts/install.sh:2:# hexpm_mcp installer — generated by tinfoil 0.2.22
scripts/install.ps1:1:# hexpm_mcp installer -- generated by tinfoil 0.2.22

Cosmetic, but it lands in every consumer's repo, and a non-ASCII character in a
shell script header is the kind of thing that occasionally surprises tooling.
-- in both is the safer default.