Update string.go

[ipsegs]

fix for panic error while using the jamctl get command.

[ipsegs]

Getting this error while testing the jamctl get command:
panic: runtime error: slice bounds out of range [:9341] with length 9340

goroutine 1 [running]:
github.com/b-nova-techhub/jamctl/pkg/util.SubstringBetween({0xc00001aa00, 0x247c}, {0xc0001a5b70?, 0x10}, {0xc0001a5b50, 0x11})
/mnt/c/Users/SegunAdebayo/Downloads/test/jamctl/pkg/util/string.go:25 +0x19f
github.com/b-nova-techhub/jamctl/pkg/gen.getHeader({0xc00001aa00, 0x247c})
/mnt/c/Users/SegunAdebayo/Downloads/test/jamctl/pkg/gen/gen.go:52 +0x118
github.com/b-nova-techhub/jamctl/pkg/gen.getFrontMatter({0xc00001aa00?, 0x7f1eca030108?})
/mnt/c/Users/SegunAdebayo/Downloads/test/jamctl/pkg/gen/gen.go:47 +0x1e
github.com/b-nova-techhub/jamctl/pkg/gen.Generate({0xc000037d80, 0x3, 0xc000178f00?})
/mnt/c/Users/SegunAdebayo/Downloads/test/jamctl/pkg/gen/gen.go:29 +0xdd
github.com/b-nova-techhub/jamctl/cmd.get(0xef0720?, {0xc000169230?, 0x1?, 0x1?})
/mnt/c/Users/SegunAdebayo/Downloads/test/jamctl/cmd/get.go:25 +0x36
github.com/spf13/cobra.(*Command).execute(0xef0720, {0xc000169200, 0x1, 0x1})
/home/shegedo/Projects/goproj/pkg/mod/github.com/spf13/cobra@v1.2.0/command.go:863 +0x663
github.com/spf13/cobra.(*Command).ExecuteC(0xef0480)
/home/shegedo/Projects/goproj/pkg/mod/github.com/spf13/cobra@v1.2.0/command.go:977 +0x3bd
github.com/spf13/cobra.(*Command).Execute(...)
/home/shegedo/Projects/goproj/pkg/mod/github.com/spf13/cobra@v1.2.0/command.go:905
github.com/b-nova-techhub/jamctl/cmd.Execute(...)
/mnt/c/Users/SegunAdebayo/Downloads/test/jamctl/cmd/cmd.go:24
main.main()
/mnt/c/Users/SegunAdebayo/Downloads/test/jamctl/main.go:9 +0x25