renamed html files to .shtml files in server/staging/ssi

diff --git a/server/staging/ssi/footer.html b/server/staging/ssi/footer.shtml
similarity index 100%
rename from server/staging/ssi/footer.html
rename to server/staging/ssi/footer.shtml

diff --git a/server/staging/ssi/header.html b/server/staging/ssi/header.shtml
similarity index 100%
rename from server/staging/ssi/header.html
rename to server/staging/ssi/header.shtml

diff --git a/server/staging/ssi/index.html b/server/staging/ssi/index..shtml
similarity index 100%
rename from server/staging/ssi/index.html
rename to server/staging/ssi/index..shtml