libcurl-security.3: fix typo

Fixed minimal typo.

Closes curl#12437

docs/libcurl/libcurl-security.3

@@ -68,7 +68,7 @@ plain text anywhere.
 Many of the protocols libcurl supports send name and password unencrypted as
 clear text (HTTP Basic authentication, FTP, TELNET etc). It is easy for anyone
 on your network or a network nearby yours to just fire up a network analyzer
-tool and eavesdrop on your passwords. do not let the fact that HTTP Basic uses
+tool and eavesdrop on your passwords. Do not let the fact that HTTP Basic uses
 base64 encoded passwords fool you. They may not look readable at a first
 glance, but they are easily "deciphered" by anyone within seconds.