replace strings.Title to cases.Title

[EinfachePhy]

strings.Title is Deprecated, because the rule Title uses for word boundaries does not handle Unicode

[kevwan]

LGTM.

[waltcow]

NGTM, All code generate with new goctl can not match with the old generated code in method name

func TestString_Camel(t *testing.T) {
	ret := From("ThisCamel").ToCamel()
	assert.Equal(t, "ThisCamel", ret)
}

=== RUN TestString_Camel
string_test.go:46:
Error Trace: /tools/goctl/util/stringx/string_test.go:46
Error: Not equal:
expected: "ThisCamel"
actual : "Thiscamel"

    	            	Diff:
    	            	--- Expected
    	            	+++ Actual
    	            	@@ -1 +1 @@
    	            	-ThisCamel
    	            	+Thiscamel
    	Test:       	TestString_Camel

--- FAIL: TestString_Camel (0.00s)

Expected :ThisCamel
Actual :Thiscamel