Upgrade libz-sys to 1.1.2

[shepmaster]

The current version has warnings that become errors on new versions of clang shipped in XCode:

warning: src/zlib/gzlib.c:214:15: error: implicitly declaring library function 'snprintf' with type 'int (char *, unsigned long, const char *, ...)' [-Werror,-Wimplicit-function-declaration]
warning:         (void)snprintf(state->path, len + 1, "%s", (const char *)path);
warning:               ^
warning: src/zlib/gzlib.c:214:15: note: include the header <stdio.h> or explicitly provide a declaration for 'snprintf'
warning: 1 error generated.

warning: src/zlib/gzwrite.c:428:11: error: implicitly declaring library function 'vsnprintf' with type 'int (char *, unsigned long, const char *, __builtin_va_list)' [-Werror,-Wimplicit-function-declaration
warning:     len = vsnprintf(next, state->size, format, va);
warning:           ^
warning: src/zlib/gzwrite.c:428:11: note: include the header <stdio.h> or explicitly provide a declaration for 'vsnprintf'
warning: 1 error generated.

r? @Mark-Simulacrum

/cc @joshtriplett

[Mark-Simulacrum]

@bors r+ rollup=never

[bors]

📌 Commit 15bd236 has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 15bd236 with merge 4e8a8b4...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: Mark-Simulacrum
Pushing 4e8a8b4 to master...