Update tcell dependency because I broke mouse support

I recently submitted a patch to tcell to address a problem parsing the
setab background color terminfo rule when running under
TERM=xterm-16color. But @tslocum spotted that I broke mouse support as a
result... This is now fixed in tcell.

go.mod

@@ -35,6 +35,6 @@ require (
 	gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 // indirect
 )
 
-replace github.com/gdamore/tcell => github.com/gcla/tcell v1.1.2-0.20200915024252-1519b137068a
+replace github.com/gdamore/tcell => github.com/gcla/tcell v1.1.2-0.20200927150251-decc2045f510
 
 replace github.com/pkg/term => github.com/gcla/term v0.0.0-20191015020247-31cba2f9f402

go.sum

@@ -48,6 +48,8 @@ github.com/gcla/tcell v1.1.2-0.20200115035344-b90e69b9dbe0 h1:6fMu73gAbCSAYAGFhM
 github.com/gcla/tcell v1.1.2-0.20200115035344-b90e69b9dbe0/go.mod h1:vxEiSDZdW3L+Uhjii9c3375IlDmR05bzxY404ZVSMo0=
 github.com/gcla/tcell v1.1.2-0.20200915024252-1519b137068a h1:jjb/Tr5RxePgvERWFtwUDOU0Kn3RqGhc0HjPu1qeemU=
 github.com/gcla/tcell v1.1.2-0.20200915024252-1519b137068a/go.mod h1:vxEiSDZdW3L+Uhjii9c3375IlDmR05bzxY404ZVSMo0=
+github.com/gcla/tcell v1.1.2-0.20200927150251-decc2045f510 h1:TlEZ0DHOvn0P79nHtkfemw7XFn2h8Lacd6AZpXrPU/o=
+github.com/gcla/tcell v1.1.2-0.20200927150251-decc2045f510/go.mod h1:vxEiSDZdW3L+Uhjii9c3375IlDmR05bzxY404ZVSMo0=
 github.com/gcla/term v0.0.0-20191015020247-31cba2f9f402 h1:d8cpYNgYjXDjvrdnSaFy4+o1D3BpPUKTBIcijrBKv4c=
 github.com/gcla/term v0.0.0-20191015020247-31cba2f9f402/go.mod h1:YCPU+G35BFc/575HWMl8oeqq+dTbunufWbWaV0Y2sqY=
 github.com/gcla/termshark v1.0.0 h1:3jDyqYHeGIfN2khlAfWmJzoJJTh6Iau2mz81nakLBPk=