allow "=" in addition to "==" for SQL compat

[mccanne]

No description provided.

[philrz]

Verified in super commit 6485155.

Before:

$ super -version
Version: v1.18.0-88-gbb910533

$ super -c "SELECT CustomerID FROM "customers.csv" WHERE Country='Mexico';"
super: error parsing SuperPipe at line 1, column 51:
SELECT CustomerID FROM customers.csv WHERE Country='Mexico';
                                              === ^ ===

Now:

$ super -version
Version: v1.18.0-90-g64851555

$ super -c "SELECT CustomerID FROM "customers.csv" WHERE Country='Mexico';"
{CustomerID:2.}
{CustomerID:3.}
{CustomerID:13.}
{CustomerID:58.}
{CustomerID:80.}

Thanks @mccanne!